--- /dev/null
+// Copyright © 2011 Moritz Hanke
+
+// Based on Lossless Data Compression. Blue Book. Issue 1. May 1997.
+// CCSDS 121.0-B-1
+//
+// http://public.ccsds.org/publications/bluebooks.aspx
+// http://public.ccsds.org/publications/archive/121x0b1c2.pdf
+
+// Compression Identification Packet (optinal)
+// The CIP is used to configure the decompressor in case no configuration
+// data is available.
+// It is comprised of the cip Primary Header (as described in "CCSDS Space
+// Packet Protocol Blue Book") and the Packet Data Field.
+
+enum cip_packet_type {
+
+ TELEMETRY, // reporting
+ TELECOMMAND, // requesting (makes no sense for compression)
+};
+
+enum cip_sequence_flag {
+
+ CONTINUE = 0,
+ FIRST = 1,
+ LAST = 2,
+ UNSEGMENTED = 3,
+};
+
+enum cip_compression_technique {
+
+ NO = 0, // no compression is used
+ LOSSLESS = 1, // lossless compression is used
+};
+
+enum cip_predictor_type {
+
+ BYPASS_P = 0, // bypass predictor
+ UNIT_DELAY_P = 1, // unit delay predictor
+ APP_SPECIFIC_P = 7, // application-specific predictor
+};
+
+enum cip_mapper_type {
+
+ STANDARD_M = 0, // standard prediction error mapper as described in the reference
+ APP_SPECIFIC_M = 3, // application-specific mapper
+};
+
+enum cip_data_sense {
+
+ TWOS_COMPLEMENT = 0, // two's complement
+ POSITIVE = 1, // positive (mandatory if preprocessor is bypassed)
+};
+
+enum entropy_coder_option {
+
+ OPTION_S = 1, // for resolution n <= 8
+ OPTION_M = 2, // for resolution 8 < n <= 16
+ OPTION_L = 3, // for resolution 16 < n <= 32
+};
+
+struct cip_header {
+
+ //----------------------------
+ // Packet Primary Header data
+ //----------------------------
+
+ char packet_version_number; // Packet Version Number
+
+ // Packet Identification
+ enum cip_packet_type type; // Packet Type
+ char secondary_header_available; // Sequence Header Flag
+ unsigned apid; // Application Process Identifier
+
+ // Packet Sequence Control
+ enum cip_sequence_flag sequence_flag; // Sequence Flags
+ unsigned sequence_count; // Packet Sequence Count
+ // in case of a TELECOMMAND type cip
+ // data package this contains the
+ // Packet Name
+
+ unsigned data_length; // length of the Packet Data Field - 1 in byte
+};
+
+struct cip_preprocessor_configuration {
+
+ char preprocessor_present; // Preprocessor Status (0 - absent, 1 - present)
+
+ enum cip_predictor_type predictor_type; // Predictor type (undefined if preprocessor is absent)
+
+ enum cip_mapper_type mapper_type; // Mapper type (undefined if preprocessor is absent)
+
+ char block_size; // Block size (8, 16 or application specific)
+
+ enum cip_data_sense data_sense;
+
+ char resolution; // Input data sample resolution (1-32)
+};
+
+struct cip_entropy_coder_configuration {
+
+ enum entropy_coder_option option; // Entropy Coder option
+
+ unsigned num_cds_per_packet; // Number of coded data sets per packet
+};
+
+struct cip_source_data_field {
+
+ unsigned grouping_data_length; // Grouping Data Length
+
+ enum cip_compression_technique compression_technique; // Compression Technique Identification
+
+ unsigned reference_sample_interval; // Reference Sample Interval
+ // - in case a preprocessor is
+ // used that requires a
+ // reference sample
+ // - in case of the zero-block
+ // option it contains the
+ // interval of input data sample
+ // blocks
+
+ struct cip_preprocessor_configuration preprocessor_config; // Preprocessor Configuration
+
+ struct cip_entropy_coder_configuration entropy_coder_config; // Entropy Coder Configuration
+};
+
+struct cip {
+
+ struct cip_header header; // Information from the Primary Header
+ struct cip_source_data_field sdf; // Information on the data
+};
+
+void * decode_cip(void * buffer, struct cip * cip);
+ // data: buffer starting with a cip
+ // cip: in case cip is not NULL the configuration information
+ // contained in the cip is written to it
+ // returns a pointer to the compressed data without the cip
+ // returns NULL in case an error occured while decoding
--- /dev/null
+// Copyright © 2011 Moritz Hanke
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "bit_macros.h"
+#include "cip.h"
+
+// decode Packet Primary Header
+void * decode_pph(void * buffer, struct cip * cip);
+
+// decode Secondary Header
+void * decode_sh(void * buffer, struct cip * cip);
+
+// decode Source Data Field
+void * decode_sdf(void * buffer, struct cip * cip);
+
+// decode Preprocessor Parameters
+void * decode_preprocessor(void * buffer, struct cip * cip);
+
+// decode Entopy Coder Parameters
+void * decode_entropy_coder(void * buffer, struct cip * cip);
+
+// decode Instrument Configuration
+void * decode_instrument_configuration(void * buffer, struct cip * cip);
+
+void * decode_cip(void * buffer, struct cip * cip) {
+
+ void * pdf; // Packet Data Field
+ void * sdf; // Source Data Field
+ void * cds; // Coded data sets
+
+ pdf = decode_pph(buffer, cip);
+
+ if (cip->header.secondary_header_available)
+ sdf = decode_sh(pdf, cip);
+ else
+ sdf = pdf;
+
+ cds = decode_sdf(sdf, cip);
+
+ if ((char*)cds > (char*)pdf + cip->header.data_length + 1) {
+
+ fprintf(stderr, "Packet Data Field is bigger than specified in CIP Packet Primary Header\n");
+ exit(EXIT_FAILURE);
+ }
+
+ return (char*)pdf + cip->header.data_length + 1;
+}
+
+// decode Primary Header
+void * decode_pph(void * buffer, struct cip * cip) {
+
+ char * cip_buf = buffer;
+
+ // Packet Version Number
+
+ cip->header.packet_version_number = (cip_buf[0] >> 5) & B3 ;
+
+ if (cip->header.packet_version_number != 0) {
+
+ fprintf(stderr, "Undefined Packet Version Number\n");
+ exit(EXIT_FAILURE);
+ }
+
+ // Packet Identification
+ {
+ // Packet Type
+
+ cip->header.type = ((cip_buf[0] >> 4) & B1)?TELECOMMAND:TELEMETRY;
+
+ // is a Secondary Header available
+
+ cip->header.secondary_header_available = (cip_buf[0] >> 3) & B1;
+
+ // Application Process Identifer
+
+ cip->header.apid = ((unsigned)(cip_buf[0] & B3) << 8) | cip_buf[1];
+ }
+
+ // Packet Sequence Control
+ {
+ // Sequence Flags
+
+ cip->header.sequence_flag = (cip_buf[2] >> 6) & B2;
+
+ // Packet Sequence Count or Packet Name
+
+ assert(sizeof(unsigned) > 2);
+
+ cip->header.sequence_count = ((unsigned)(cip_buf[2] & B6) << 8) |
+ cip_buf[3];
+ }
+
+ // Packet Data Length
+
+ cip->header.data_length = ((unsigned)cip_buf[4] << 8) | cip_buf[5];
+
+ return (char*)cip + 6; // the Packet Primary Header has a size of 48
+ // bits
+}
+
+void * decode_sh(void * buffer, struct cip * cip) {
+
+ // The Secondary Header contains information like time and position
+ // or attitude of a spacecraft.
+ // The handling of a Secondary Header is currently not implemented.
+
+ fprintf(stderr, "Compression Identification Packet contains a Secondary Header\n");
+ exit(EXIT_FAILURE);
+
+ return buffer;
+}
+
+void * decode_sdf(void * buffer, struct cip * cip) {
+
+ char * sdf = buffer;
+
+ // Grouping Data Length (number of packets containing compressed data)
+
+ cip->sdf.grouping_data_length = (((unsigned)(sdf[0] & B4) << 8) |
+ sdf[1]) + 1;
+
+ // check whether a compression is used for the current group
+
+ if (sdf[2] > 1) {
+
+ fprintf(stderr, "Undefined compression technique\n");
+ exit(EXIT_FAILURE);
+ }
+
+ cip->sdf.compression_technique = sdf[2];
+
+ // Reference Sample Interval
+
+ cip->sdf.reference_sample_interval = sdf[3]+1;
+
+
+ if (cip->sdf.compression_technique == LOSSLESS) {
+
+ // decode Preprocessor Parameters
+ sdf = decode_preprocessor(sdf, cip);
+ }
+
+ // decode Entropy Coder Parameters
+ sdf = decode_entropy_coder(sdf, cip);
+
+ // decode Instrument Configuration
+ sdf = decode_instrument_configuration(sdf, cip);
+
+ return sdf;
+}
+
+void * decode_preprocessor(void * buffer, struct cip * cip) {
+
+ char * sdf = buffer;
+
+ unsigned header;
+
+ // check for correct header
+ header = (sdf[0] >> 6) & B2;
+ if (header != 0) {
+
+ fprintf(stderr, "Wrong header for preprocessor field\n");
+ exit(EXIT_FAILURE);
+ }
+
+ // get preprocessor presents
+ cip->sdf.preprocessor_config.preprocessor_present = (sdf[0] >> 5) & B1;
+
+ // if a preprocessor is present
+ if (cip->sdf.preprocessor_config.preprocessor_present) {
+
+ // Predictor type
+ switch ((sdf[0] >> 2) & B3) {
+
+ case (0):
+ cip->sdf.preprocessor_config.predictor_type = BYPASS_P;
+ break;
+ case (1):
+ cip->sdf.preprocessor_config.predictor_type = UNIT_DELAY_P;
+ break;
+ case (7):
+ cip->sdf.preprocessor_config.predictor_type = APP_SPECIFIC_P;
+ break;
+ default:
+ fprintf(stderr, "Invalid predictor type\n");
+ exit(EXIT_FAILURE);
+ };
+
+ // Mapper type
+ switch (sdf[0] & B2) {
+
+ case (0):
+ cip->sdf.preprocessor_config.mapper_type = STANDARD_M;
+ break;
+ case (3):
+ cip->sdf.preprocessor_config.mapper_type = APP_SPECIFIC_M;
+ break;
+ default:
+ fprintf(stderr, "Invalid mapper type\n");
+ exit(EXIT_FAILURE);
+ };
+ }
+
+ // Block size (J)
+ switch ((sdf[1] >> 6) & B2) {
+
+ case (0):
+ cip->sdf.preprocessor_config.block_size = 8;
+ break;
+ case (1):
+ cip->sdf.preprocessor_config.block_size = 16;
+ break;
+ case(3):
+ fprintf(stderr, "Missing implementation for application-specific block size\n");
+ exit(EXIT_FAILURE);
+ default:
+ fprintf(stderr, "Invalid block size\n");
+ exit(EXIT_FAILURE);
+ };
+
+ // Data sense
+ cip->sdf.preprocessor_config.data_sense = (sdf[1] >> 5) & 1;
+
+ // check whether preprocessor presents and data sense match
+ if (!cip->sdf.preprocessor_config.preprocessor_present &&
+ cip->sdf.preprocessor_config.data_sense != POSITIVE) {
+
+ fprintf(stderr, "If no preprocessor is present, the data sense has to be positive.\n");
+ exit(EXIT_FAILURE);
+ }
+
+ // Input data sample resolution
+ cip->sdf.preprocessor_config.resolution = (sdf[1] & B5) + 1;
+
+ return (char*)buffer + 2; // the preprocessor field has a size of 2 byte
+}
+
+void * decode_entropy_coder(void * buffer, struct cip * cip) {
+
+ char * sdf = buffer;
+
+ unsigned header;
+
+ // check for correct header
+ header = (sdf[0] >> 6) & B2;
+ if (header != 1) {
+
+ fprintf(stderr, "Wrong header for entropy coder field\n");
+ exit(EXIT_FAILURE);
+ }
+
+ // Entropy Coder option
+ switch ((sdf[0] >> 4) & B2) {
+
+ case (1):
+ if (cip->sdf.preprocessor_config.resolution > 8) {
+
+ fprintf(stderr, "Entropy coder option does not match input data sample resolution\n");
+ exit(EXIT_FAILURE);
+ }
+ cip->sdf.entropy_coder_config.option = OPTION_S;
+ break;
+ case (2):
+ if ((cip->sdf.preprocessor_config.resolution <= 8) ||
+ (cip->sdf.preprocessor_config.resolution > 16)) {
+
+ fprintf(stderr, "Entropy coder option does not match input data sample resolution\n");
+ exit(EXIT_FAILURE);
+ }
+ cip->sdf.entropy_coder_config.option = OPTION_M;
+ break;
+ case (3):
+ if ((cip->sdf.preprocessor_config.resolution <= 16) ||
+ (cip->sdf.preprocessor_config.resolution > 32)) {
+
+ fprintf(stderr, "Entropy coder option does not match input data sample resolution\n");
+ exit(EXIT_FAILURE);
+ }
+ cip->sdf.entropy_coder_config.option = OPTION_L;
+ break;
+ default:
+ fprintf(stderr, "Invalid entropy coder option\n");
+ exit(EXIT_FAILURE);
+ };
+
+ assert(sizeof(unsigned) > 2);
+
+ // Number of coded data sets per packet
+ cip->sdf.entropy_coder_config.num_cds_per_packet =
+ (((unsigned)(sdf[0] & B4) << 8) | sdf[1]) + 1;
+
+ return (char*)buffer + 2; // entropy coder field has a size of 2 byte
+}
+
+void * decode_instrument_configuration(void * buffer, struct cip * cip) {
+
+ // Instrument Configuration is mission specific.
+ // This implementation assumes that there is no.
+ // In an one is added later, the first 2 bits of buffer have to 10.
+
+ return buffer;
+}