Abstract: Characters that are not among those recognized for use in page messages are encoded using a subset of the recognized printable characters to enable the data comprising a page object to be transmitted over a paging channel. In one preferred form of the invention, a subset of the recognized printable characters are designated as encoding characters for use in encoding data that includes characters not among the recognized printable character set. Further, each time that one of the encoding characters occurs in the input data, the byte representing that character must also be encoded. To encode the characters, the byte is divided into nibbles. Each nibble is a hexadecimal digit that is encoded using one of the 16 encoding characters. If a byte of the input data repeats more than four times in succession, it is run length encoded (RLE) during the encoding process to compress the encoded data.

Abstract: In order to reduce the size of the memory employed to store firmware, the firmware is written in virtual control words which are then reduced by allotting them to a primary control word memory and at least one secondary control word memory which is addressed by a field in the primary control word memory. A virtual set of secondary control words are each divided into a plurality of fields, and each field of each secondary virtual control word is marked as guarded or "don't care". If a field is marked as "don't care", the function represented by the virtual control word will perform properly no matter what the content of that field. Virtual control word pairs are then examined to ascertain if they can be combined into a single control word.

Abstract: An adaptive display refresh and data compression solution for use in an RF network environment is described, where a network controller and portable terminals maintain an adaptive history of commonly used past information in order that it may be repeated quickly and communication speeds can be increased. A network controller maintains a separate history for each of the terminals in the RF network, and transmits a coded reference for the activities that are contained in the history, which is stored in the memory of both the controller and the portable terminal. Terminals and the controller additionally may negotiate to determine the data compression features which will be supported in communication between the two devices. Data is compressed according to the present invention by utilizing a hybrid run length and sliding dictionary compression scheme.

Abstract: A method for encoding an input data stream of source symbols to produce an output sequence of pointers is disclosed. An initial part of the input data stream is encoded as a LITERAL.sub.-- POINTER by a compressor. A LITERAL.sub.-- POINTER includes at least one data byte from the data stream. A subsequent part of the input data stream is encoded as a COPY.sub.-- POINTER. The COPY.sub.-- POINTER includes a count and a displacement pointing to a history-buffer within the compressor. All succeeding data bytes from the input data stream are encoded as LITERAL.sub.-- POINTERs and COPY.sub.-- POINTERs in an alternating fashion, such that an encoded output sequence output by the compressor includes a string of pointers alternating between LITERAL.sub.-- POINTERs and COPY.sub.-- POINTERs.

Abstract: To compress data at high speed, a search character is input to a write buffer 56 in sequence. Each of content addressable memory (CAM) cell rows compares the search character with character data stored therein and outputs the comparison result through a match line MATCH to a comparison result control circuit 60 every time. The comparison result is held in sequence to latches 82 and 84. When a signal ORFB input to a signal generation circuit 64 is low, the circuit 86 outputs the logical product between the output of the latch 82 and the output of the latch 88 of the preceding stage to a priority encoder 74 through a latch 88 and also to an OR circuit 90. When the signal ORFB is high, the circuit 86 outputs the logical product between the output of the latch 82 and the output of the latch 84 of the preceding stage to the priority encoder 74 through the latch 88 and also to the OR circuit 90.

Abstract: A data encoding and decoding device and method uses simple algorithms and keeps encoding error to a minimum. The data encoding device includes an original data splitting section for splitting data into "higher order data" and "lower order data," which represents the most significant portion of a digital data sample and the least significant portion of the digital data sample, respectively. Further, a differential calculation section calculates a difference between successive samples of the higher order data, and a number-of-items calculation section determines the number of data samples in the input data series. The lower order data and the differential data are then combined to obtain the encoded data.

Abstract: A data compression and decompression apparatus and method providing a high compression ratio. The data compressing apparatus includes, for example, an obtaining section, a first coding section, a first controlling section, a judging section, a second coding section, and a second controlling section. Characters are obtained one after another from a compression target. A code is then output corresponding to the character when the character and a predetermined number of characters are not identical. Subsequently, the number of characters obtained are counted when the character and the predetermined number of characters are identical, and a code corresponding to the number of characters counted is output when the character obtained is not identical with the predetermined number of characters.

Abstract: A method for compression of digital data in a computer having a processor and a memory, wherein a group of consecutive bits having the same binary value is represented by a result number corresponding to the number of the consecutive bits. The method involves the following steps. A block of digital data to be compressed is provided. A bit detect selection parameter determines a bit value to be counted for counting consecutive bits. The processor is instructed to count from a first end of the block of digital data toward a second end of the block of digital data the number of consecutive bits having the bit value determined by the bit detect selection parameter. The number of bits so counted is stored, and the bit detect selection parameter is toggled. The processor is then instructed to count from the last bit counted toward the second end of the block of digital data the number of bits having the bit value determined by the current bit detect selection parameter.

Abstract: A method of reducing a number of bits required to transmit a digital signal using a PPP protocol is disclosed. The PPP protocol uses a predetermined byte for signalling. When that byte occurs, the following byte indicates signalling or alternatively, indicates a data byte having a value of the signalling byte. A value in the signalling byte is used to indicate a data byte, and other values are encoded to represent two or more signalling bytes within a predetermined spacing. Due to the look-ahead requirements, a time lag is introduced.

Abstract: A method for compressing a data stream, where a first portion of the data stream is read into a window having a history buffer and look-ahead buffer. An index, based on a fourth portion of the data stream in the look-ahead buffer is used to select an entry in a pointer array. An initial entry in a record array is selected based on the pointer array entry. A third portion of the data stream is selected. The third portion is compared to a second portion in the look-ahead buffer. If the third portion does not match the second portion, then a subsequent entry in the record array is selected, and the is designated as the initial entry. These steps are repeated until either the third portion matches the second portion, or no more entries are left in the record array. When there are no more entries left in the record array, the second portion is written to the output file, and the first portion read into the window is incremented by a predetermined amount.

Abstract: A method and apparatus for losslessly compressing binary data using a technique referred to as Double Run-Length Encoding (DRLE). DRLE has particular application to the compression of gray-scale data as it is being processed for printing by a laser printer or other continuous raster scan device. DRLE records repeating patterns of ones and zeros with little computational complexity. Compression ratios that may be an order of magnitude or more are obtained frequently on data that may not compress well using traditional Run-Length Encoding (RLE). DRLE uses a sequential history of order-pairs that denote variable-length patterns of zeros and ones, and then encodes these patterns as they repeat themselves.

Abstract: An input data sequence is divided into fixed-length source segments, and each source segment is predicted from preceding data. The data are coded as a sequence of coded segments, each designating a non-negative number of correctly predicted segments and a non-negative number of literal segments. The literal segments are inserted into the coded data among the coded segments. The coded data are decoded by decoding each coded segment, predicting the designated number of correctly predicted segments from previously decoded data, and copying the literal segments. The length of the coded segments may vary according to the number of consecutive correctly predicted segments. The prediction rule, or the original data, may be modified under certain conditions, in order to increase the predictability of the source segments.

Abstract: A method of compressing a stream of raw data including the steps of providing a memory device having compression active state and a compression inactive state, inputting a raw data segment into the memory device, generating a compressed data segment based on the raw data segment, creating output data based on the compressed data segment when the memory device is in the compression active state, otherwise based on the raw data segment when in the memory device is the compression inactive state, calculating a compression coefficient, and setting the state of the memory device based on the compression coefficient, such that compressed data is output only when compression has recently proven effective, and raw data is output when compression has recently proven ineffective. The method may also include decompression of the output data.

Abstract: According to the present invention, for encoding input signals, the input signals are transformed into frequency components, and the frequency components are separated into a first signal composed of tonal components and a second signal composed of other components. The first and second signals are encoded respectively, and code strings for transmission or recording are generated on the basis of encoded signals resulting from first and second encoding. For example, only the first signal is encoded and the code string is caused to include partial information strings grouped so as to have common values on the basis of at least one of reference parameters pertaining to the signal separation and parameters pertaining to the first encoding. Thus, more efficient encoding than in the conventional technique can be realized.

Abstract: For saving memory space, the use of a sophisticated compressor is to be preferred to a simple reduction of the sampling frequency. However, for very high compression rates the total number of calculations is such that the compressor would no longer be capable of following the timing with which the samples arrive. Particularly in the case of a telephone/recorder where sound messages are received in separate call elements of limited duration, the invention consists of finally compressing once again samples that one has not been able to compress in real time at a sufficiently high compression rate.

Abstract: A device for coding a series of symbols based on a multi-level arithmetic coding scheme includes a coding unit for coding the symbols based on frequency of occurrence of the symbols and orders of the symbols according to the frequency of occurrence, a context holding unit for storing the frequency of occurrence and the orders, a context updating unit for updating the frequency of occurrence and the orders upon receiving a control signal, and a controlling unit for sending the control signal when one of the symbols is coded and a cumulative frequency is less than a predetermined value, wherein the cumulative frequency is a sum of the frequency of occurrence for all of the symbols.

Abstract: A data processing apparatus has a dictionary control unit in which pieces of dictionary data stored in a dictionary buffer are compared with pieces of input data to be compressed input one after another, a piece of particular dictionary data agreeing with a piece of particular input data is expelled from the dictionary buffer, the dictionary data stored in the dictionary buffer are placed close together in a direction, and the particular input data is written in the dictionary buffer.

Abstract: A dual stage data lossless compressor for optimally compressing bit mapped imaged data. The first stage run length compresses data bits representing pixel positions along a scan line of a video image to data units of fixed length. The units alternate to represent runs of alternate video image data values. The run length compressed data units are subject to second stage compression using a sliding window Lempel-Ziv compressor. The output from the Lempel-Ziv compressor includes raw tokens of fixed length and compressed tokens of varying lengths. The combination of a run length precompressor and a sliding window Lempel-Ziv post compressor, in which the run length compressor output is a succession of data units of fixed length, provides an optimum match between the capabilities and idiosyncracies of the two compressors, and related decompressors, when processing business form data images.

Abstract: A real-time method for improving data compression. The correlation between data characters being provided a modem (10) is determined. Two measures are used to determine the correlation between data characters: the shape of tree(s) (6) in encoding table (16) and the compression ratio (96). Once the correlation between data characters is determined using the two measures, the size of the encoding table (16) can be changed. If the data characters are not correlated, meaning the data is random or pseudo-random, the size of the encoding table is decreased. If the data characters are highly correlated, changing the size of the encoding table reduces time spent attempting to compress incompressible data and increases data compression for compressible data.

Abstract: A method of performing Ziv-Lempel type data compression while preserving in the compressed records any sort ordering of the uncompressed records. The method assigns the necessary ordered numbering to the code words for character strings in a static compression dictionary even though the dictionary is structured so that all children of the same parent have sequential index numbering. The children of a parent are in collating sequence order, and adjacent children that are nonadjacent in the collating sequence have a conceptual epsilon entry between them, which entry represents a match on the parent and a direction in the collating sequence. Code words for actual children are formed by using a dictionary entry index to locate a translation table entry containing a code word. Code words for epsilon entries are formed by using an entry index for an actual child to locate a translation table entry and then adding or subtracting one to or from the code word in the entry.

Abstract: A system for compressing digital data at one byte-per-cycle throughput by removing redundancy before storage or transmission. The system includes an improved Ziv-Lempel LZ1 process that uses a history buffer to save the most recent source string symbols for use in encoding the source symbols as "match-length" and "match-offset" tokens. The match-length code symbols are selected from two groups of buckets that are assigned variable-length prefixes for the shorter, more probable match-lengths and a fixed-length prefix code for the longer, less probable match-lengths. This exploits a transition from Laplacian match-length probability distribution to Uniform match-length probability distribution for longer match-lengths. The offset code field length is reduced during start-up to improve start-up compression efficiency during filling of the history buffer. The match-length code book is limited to a maximum value T<256 to limit latency and simplify the process.

Abstract: Repetitive data and non-repetitive data, including periods of no information, is encoded prior to transmission or storage in digital form to minimize the memory space required for storage or the time required to transmission. Repetition, partial repetition, and near repetition is encoded in a form indicating the occurrence of repetition, its characteristics and its duration. The existence and size of repeated patterns in the data is dynamically determined. When repetition is detected, non-repetitive data is inserted into the data stream and repeated data is removed from the data stream. To this non-repeated data in the data stream are added a coded repeated pattern sample, an identification preamble signal, an instruction signal for decoding purposes, a period count signal, a mask signal, and a repeat count signal. All necessary data elements are combined and assembled to produce compressed data. A receiver utilizes these coded and uncoded data elements to regenerate complete original data.

Abstract: A method of data compression includes means to accelerate a direct query thereof. Input data are transformed into a multilevel n-ary tree structure wherein each leaf node corresponds to the creation of a memory storing unique occurrences of a particular data body, and each non-leaf node corresponds to a memory storing unique occurrences associated with its child nodes, whether leaf or non-leaf types. To accelerate a determination as to the solution of a query of the data, one or more pointers are further stored at each memory level, the pointers at least including those used to identify the parent of each child node and the children of each parent. In the preferred embodiment additional pointers are further stored in conjunction with each non-leaf node, these being used to identify other locations corresponding to unique occurrences derived through the same child nodes.

Abstract: The invention relates to a process and an apparatus for compacting binary informations, then reconstructing and processing them in delayed time or with a time lag. It consists of compacting the binary informations by posting during a given cycle informations received on several channels and then associating non-zero information sums with memory channel numbers. It then consists solely of reconstructing the useful informations by coding them in cycle table form. Applied to nuclear fission, this invention consists of delayed time processing of tables in order to determine the proportion of neutrons induced by a fission and neutrons coming from other reactions.

Abstract: Methods for compressing data including methods for compressing highly randomized data are disclosed. Nibble encode, distribution encode, and direct bit encode methods are disclosed for compressing data which is not highly randomized. A randomized data compression routine is also disclosed and is very effective for compressing data which is highly randomized. All of the compression methods disclosed operate on a bit level and accordingly are insensitive to the nature or origination of the data sought to be compressed. Accordingly, the methods of the present invention are universally applicable to any form of data regardless of its source of origination.

Abstract: A system for transmitting compressed data for multiple channels or contexts from a single node which system reduces memory utilization without significant adverse effect on compression ratio by providing a separate history buffer for each channel, with a single hash table being provided for generating potential match addresses in the history buffer for at least selected ones of the channels. A single chain table may also be provided, the chain table having a single offset address for the corresponding offset addresses in the buffers for the selected channels. Collisions in the common hash table may be reduced by including channel address or the like as an additional input to the hash table, thereby biasing the address outputs therefrom.

Abstract: Disclosed is a method and system for data compression. In a preferred embodiment, an input stream of data bytes are compressed into an encoded stream using an LZ77-based scheme. The preferred method searches for a matching sequence of already processed data bytes that is identical to a current sequence of bytes. Sequences of literals (bytes not forming part of a matching sequence) or match codes (encoded matching sequences) are identified by count values indicating the number of literals or match codes in the sequence. Preferably, the encoded stream is transmitted from a first computer to a second computer, where the encoded stream is decompressed. The method uses matching circular history buffers for compression and decompression, the history buffers being synchronized using a coherency byte included with each frame of encoded data transmitted. If an encoded frame is not received by the decompression device, the decompression device transmits a flush request to the compression device.

Abstract: A compressed data recording and/or reproducing apparatus has a compressed data reproducing system for at least reproducing digital data from one recording medium such as a magneto-optical disc in which digital data is bit-compressed and recorded and a compressed data recording system for at least recording digital data in one other recording medium such as an IC card in which digital data is bit-compressed and recorded. The compressed data recorded in the one recording medium of the reproducing system is reproduced and transmitted to the recording system. The compressed data is also bit-compressed at the same or a lower bit rate and recorded in the other recording medium. For this recording, a processing block of the bit compression is selectively deleted in accordance with a scale factor of the bit, compression.

Abstract: A class of lossless data compression algorithms use a memory-based dictionary of finite size to facilitate the compression and decompression of data. To reduce the loss in data compression caused by dictionary resets, a standby dictionary is used to store a subset of encoded data entries previously stored in a current dictionary. In a second aspect of the invention, data is compressed/decompressed according to the address location of data entries contained within a dictionary built in a content addressable memory (CAM). In a third aspect of the invention, the minimum memory/high compression capacity of the standby dictionary scheme is combined with the fast single-cycle per character encoding/decoding capacity of the CAM circuit. In a fourth aspect of the invention, a selective overwrite dictionary swapping technique is used to allow all data entries to be used at all times for encoding character strings.

Abstract: A method and apparatus for compressing inherently redundant data. A Unicode file is comprised of prefix group indicator bytes and suffix character indicator bytes and can therefore be separated into two files, one containing the prefixes and one containing the suffix characters. Then, each separate file can be separately compressed using means best suited to the characteristics of each. Because of the high degree of redundancy across the prefix group indicator bytes they can be more greatly compressed which in turn results in greater compression of the entire Unicode file. Multiple compression methodologies, equally applicable to any inherently redundant data file, can be applied to the prefix group indicator bytes to yield the best compression results. In the present invention, one commonly occurring byte, known as the master byte, is chosen and each exception to the master byte in the data file to be compressed is noted by location (l) and value (v) thus reducing the overall size of the data file.

Abstract: An apparatus and method for compressing an input sequence of data items produced by sampling a periodic waveform compresses such input sequence by searching a history buffer operable to store consecutive data items, to locate a stored sequence of consecutive data items matching the input sequence. Matching is deemed to occur when each data item in the input sequence is within non-equal upper and lower limits of its corresponding data item in the stored sequence. When a stored sequence matching the input sequence is located compressed output data is produced to represent the stored sequence and the stored sequence is again stored in the history buffer to succeed the data items already stored therein. When a stored sequence matching the input sequence is not located, a representation of the first data item in the input sequence is produced and the first data item is stored in the history buffer to succeed the data items already stored therein.

Abstract: Repetitive data and non-repetitive data, including periods of no information, is encoded prior to transmission or storage in digital form to minimize the memory space required for storage or the time required to transmission. Repetition, partial repetition, and near repetition is encoded in a form indicating the occurrence of repetition, its characteristics and its duration. The existence and size of repeated patterns in the data is dynamically determined. When repetition is detected, non-repetitive data is inserted into the datastream and repeated data is removed from the datastream. To this non-repeated data in the datastream are added a coded repeated pattern sample, an identification preamble signal, an instruction signal for decoding purposes, a period count signal, a mask signal, and a repeat count signal. All necessary data elements are combined and assembled to produce compressed data. A receiver utilizes these coded and uncoded data elements to regenerate complete original data.

Abstract: A method of transmitting data from a base transceiver station or base station to a transcoder. Prior to transmission to the base station, the data is organized in streams of frames (T1, T2, T3). The streams are assembled into groups (G1, G2, G3), and the transmission of the data to the base station starts at the start of a stream of frames (T1, T2, T3). The method includes the following operations: after activation of a channel of the base station for reception of the data frames, the first stream of frames (T1, T2, T3) received on the channel by the base station is associated with a reference number within the corresponding group of frames (G1, G2, G3); and transmission of data by the base station to the transcoder is then delayed by an amount (R.sub.1/3, R.sub.2/3) depending on the reference number and the group of frames of the first stream of frames, whereby a continuous stream of data (A1, A2, A3) is transmitted by the base station to the transcoder.

Abstract: A selective call communication system (100) includes an encoder (508) for encoding and compressing the data to form compressed data, and a controller (22) for transferring the compressed data to a selective call terminal (28). The selective call terminal (28) includes a receiver (302) for receiving the compressed data. A region detector (308) for recovering the compressed data within a predefined information region (42) and a processor (20) for processing the compressed data. The processor (20) includes an identifier (310) for identifying white spaces in the compressed data and an eliminator (312) for eliminating the white spaces being identified. A transmitter (30) for transmitting the compressed data being processed to at least one selective call receiver (40).

Abstract: A decoder circuit for generating mask patterns on a plurality of output terminals in response to multibit binary input number is described using a plurality of two-input multiplexers arranged in parallel paths to form one stage or as a tree structure consisting of several cascaded stages of binary or higher order and controlled by functions of the bits of an input number to produce a logic "1" voltage on a number of output terminals equal to the input number and a logic "0" voltage on the remaining output terminals.

Abstract: The disclosed data stream optimization process is containing two logical entities, the first being the pre-comparison optimizer component and the second being the comparison component. The pre-comparison optimizer component performs two discrete tasks. First, the input data stream is written into a next state buffer. Second, the elimination of redundancies involves detecting and removing redundant screen attributes, since the terminal's execution time for processing a screen attribute is more than that required for a data character. The comparison component contains three distinct sub-components. First, non-data constructs such as commands and orders are optimized and placed in the outgoing data stream. Second, the screen image that is represented by the data stream is compared to the existing screen image to further reduce the outgoing data stream.

Abstract: The present invention is a data compression method having an improved encoding algorithm which utilizes a token stacking technique. The essential step of the present invention encoding method is constructing a group of stacked tokens. Each stacked token has multiple fields including a substring length counter field and a backward displacement pointer field, where the former is identical among all stacked tokens for serving as the basis in constructing the group of stacked tokens, and the latter is assigned with a respective range of integers. The ranges assigned to the stacked tokens are stacked sequentially without overlapping. The encoding method further comprises the steps of determining a backward displacement pointer for a compressible substring and encoding the backward displacement pointer into a respective stacked token according to the range assigned, such that the backward displacement pointer falls within the range assigned to the respective stacked token.

Abstract: Apparatus is provided for performing two stages of high-speed compression of vector data inputs. Two input channels of vector data are compressed and encoded through a vector quantizer encoder to provide a first stage of data compression. The output of the first encoder is further decoded then compressed and encoded in a novel high-speed computing mapping means which may be implemented in the form of a look-up table. Vector quantized encoded output is double the previous data compression of a single stage. The second stage of data compression causes very little degradation of the data from the first stage of data compression.

Abstract: The compression system includes a series of pipelined data processors. Each processor has an associated memory. The body of digital data is applied serially to the first processor in the chain. The first processor analyzes pairs of data elements in its incoming signal to detect the occurrence of previously non-occurring sequences and stores those sequences in its associated memory. The output signal from the processor identifies the storage position in its associated memory of each pair of data elements in its input, whether or not those sequences have previously occurred in the data stream. Subsequent processors work with storage location signals only. Each processor provides a single output location signal for each pair of signals in its input. Each processor also determines the number of times that each incoming sequences has occurred and stores that number in association with each stored pair.

Abstract: A data decoder is described for decoding interleaved first type code words [RUNLENGTH, SIZE] and second type code words [AMPLITUDE], each first type code word serving to define a runlength of constant values preceding a variable value defined by a following second type code word. The first type code words and the second type code words are fed to respective first and second pipeline delay units 22 and 24. The output from the first pipeline delay unit 22 is fed to a state machine 26 which reads the RUNLENGTH value and generates an INSERT ZEROS signal for a period proportional to the RUNLENGTH value followed by a signal triggering reading of the second pipeline delay unit 24. The INSERT ZEROS signal and the output of the second pipeline delay unit 24 are fed to a multiplexer 28 which selects between them to generate the appropriate OUTPUT signal. A swing buffer 10 is disposed upstream of the first and second pipeline delay units 22 and 24.

Abstract: In a data compressing and decompressing apparatus, having improved efficiency and enhanced compression ratio whereby character sequence of received data is coded and decoded by referring to a dictionary related to the last character of the immediately preceding character sequence, and a character sequence which is one character extended character sequence of the coded and decompressed character sequence is registered in the dictionary in relation with the last character of the immediately preceding character sequence so that the compression ratio of the coding of data is increased.

Abstract: The use of a dynamically mapped virtual memory system permits the storage of data so that each data record occupies only the physical space required for the data. Furthermore, the data storage subsystem manages the allocation of physical space on the disk drives and does not rely on the file extent defined in the count key data format. Data compaction apparatus is provided to remove the gaps contained in the stream of count key data records received from the host processor. A data compression algorithm is then used to compress the received data into a compressed format for storage on the disk drives. It is the compacted, compressed data that is finally stored on the disk drives. Furthermore, any data record received from the host processor absent data in the user data field therein is simply listed in the virtual memory map as a null field occupying no physical space on the disk drives.

Abstract: The compression system includes a series of piplined data processors. Each processor has an associated memory. The body of digital data is applied serially to the first processor in the chain. The first processor analyzes pairs of data elements in its incoming signal to detect the occurrence of previously non-occurring sequences and stores those sequences in its associated memory. The output signal from the processor identifies the storage position in its associated memory of each pair of data elements in its input, whether or not those sequences have previously occurred in the data stream. Subsequent processors work with storage location signals only. Each processor provides a single output location signal for each pair of signals in its input. Each processor also determines the number of times that each incoming sequence has occurred and stores that number in association with each stored pair.

Abstract: A class of lossless data compression algorithms use a memory-based dictionary of finite size to facilitate the compression and decompression of data. When the current dictionary (CD) fills up with encoded character strings, it is reset thereby losing the compression information previously contained in the dictionary. To reduce the loss in data compression caused by dictionary resets, a second, standby dictionary (SD) is used to simultaneously store a subset of the encoded data entries stored in the first dictionary. The data entries in the second dictionary represent the data entries of the first dictionary that compress the greatest amount of input data. When the first dictionary is ready to be reset, the first dictionary is replaced with the second dictionary, maintaining high data compression and freeing up memory space for new encoded data strings.

Abstract: Methodology and concomitant circuitry for compacting an incoming data stream into an outgoing compacted data stream utilize a multiple, doubly-linked list and an associated class promotion data structure. The incoming data stream is partitioned into a sequence of symbols. A memory associated with the data structure stores each symbol, information regarding the recency rank of each symbol as it arrives in sequence as well as class information and pointer information for each symbol. For each symbol, the memory is checked to determine if the symbol is new or repeated. If the symbol is repeated, only the recency rank is used to form that part of the outgoing data stream associated with the new symbol. If the symbol is new, identification information is added to the symbol and both the identification information are emitted as part of the compacted stream. Memory update operations are then effected to change class, recency rank and pointer information.

Abstract: The data unpacker receives packed parallel input data words having a fixed width of m bits, and it outputs parallel data words having a variable width of n bits. An input register stores the received words and applies them to a bit shifter. The bit shifter shifts the received data by a number of bit positions indicated by a shift control signal, and the shifted data is output therefrom as a parallel output word having n valid bits. The number n for each output word is received by the unpacker as a binary number. When n.gtoreq.m, a most significant (MSB) bit portion of that number is applied as first MSB control signal. The least significant bit (LSB) portion of n is applied to an adder which adds subsequently received LSB portions to provide a running sum. When the running sum is equal to or greater than m, the adder provides a second MSB control signal, corresponding to the most significant bit of the running sum.

Abstract: A device for adaptively encoding a flow of data symbols x.sub.1, x.sub.2, . . . , x.sub.t taken within a predefined symbol family, into a compressed bit string c(s), said method including so-called modelling operations (see Modelling Unit 60) whereby the numbers of times each symbol occurs in the flow are collected in a tree architecture denoting past flow symbols considered in a predefined order according to a reordering function f(t), and Relative Efficiency Counter (REC) facilities embedded in the growing tree nodes, and tracking REC variations for both optimal coding node determination and tree updating operations. The compressed bit string is then generated by an Arithmetic Coder (64) connected to said Modelling Unit (60).

Abstract: A format converter for converting an input signal having a specified format to a digital signal of a pre-existing format, and for converting the digital signal back to the input signal automatically, loads an active data portion of the input signal into an input first-in/first-out (FIFO) buffer at a first data rate and reads the active data portion together with dummy filler samples from the FIFO at a second data rate as the digital signal. The number, location and/or values of the filler samples identify the specified format. In reverse the filler samples are stripped from the digital signal and the resulting active samples are loaded into an output FIFO at the second data rate. The stripped filler samples are used to determine the specified format of the original source of the data signal, and the active samples are read from the output FIFO at the first data rate in the specified format to reproduce the input signal.

Abstract: A method and apparatus for a processor or other system device to map processor words to an associated random access memory. In one case, processor words are mapped directly to RAM with no modification. In another case, 32-bit pixels (eight bits each of red, green, blue and alpha) are converted to or from 16-bit pixels (four bits each of red, green, blue and alpha) using an ordered dithering technique. The ordered dithering technique spatially distributes the information that would otherwise be lost by truncation. This is accomplished by replacing exact pixel values with their pseudo-random average. This reduces the required pixel storage requirements by half, while maintaining a higher image quality than would be achieved by truncation alone.

Abstract: A method of detecting certain runs of data, such as identical consecutive runs of data, is disclosed. The logical operation exclusive OR (XOR) is performed on each pair of adjacent bytes in a source string of data bytes in a single machine instruction, resulting in a comparison data string of bytes. The comparison data string is then sequentially searched for a byte which matches a predetermined byte. In the case of a search, the predetermined byte may be any value, which value is determined by the XOR of two adjacent bytes that are to be found. In the case of compression, as used in this invention, the predetermined byte has a value of zero, indicating that two adjacent bytes in the source string are identical. The sequential search occurs in a single Translate and Test (TRT) machine instruction. Once an all-zero byte is located, the subsequent byte in the comparision data string is examined.