ac.rar

#include <stdio.h> #include <stdlib.h> #include "ac.h" #define Code_value_bits 16 #define Top_value (((long)1<<Code_value_bits)-1) #define First_qtr (Top_value/4+1) #define Half (2*First_qtr) #define Third_qtr (3*First_qtr) #define Max_frequency 16383 static void output_bit (ac_encoder *, int); static void bit_plus_follow (ac_encoder *, int); static int input_bit (ac_decoder *); static void update_model (ac_model *, int); #define error(m) \ do { \ fflush (stdout); \ fprintf (stderr, "%s:%d: error: ", __FILE__, __LINE__); \ fprintf (stderr, m); \ fprintf (stderr, "\n"); \ exit (1); \ } while (0) #define check(b,m) \ do { \ if (b) \ error (m); \ } while (0) static void output_bit (ac_encoder *ace, int bit) { ace->buffer >>= 1; if (bit) ace->buffer |= 0x80; ace->bits_to_go -= 1; ace->total_bits += 1; if (ace->bits_to_go==0) { if (ace->fp) putc (ace->buffer, ace->fp); ace->bits_to_go = 8; } return; } static void bit_plus_follow (ac_encoder *ace, int bit) { output_bit (ace, bit); while (ace->fbits > 0) { output_bit (ace, !bit); ace->fbits -= 1; } return; } static int input_bit (ac_decoder *acd) { int t; if (acd->bits_to_go==0) { acd->buffer = getc(acd->fp); if (acd->buffer==EOF) { acd->garbage_bits += 1; if (acd->garbage_bits>Code_value_bits-2) error ("arithmetic decoder bad input file"); } acd->bits_to_go = 8; } t = acd->buffer&1; acd->buffer >>= 1; acd->bits_to_go -= 1; return t; } static void update_model (ac_model *acm, int sym) { int i; if (acm->cfreq[0]==Max_frequency) { int cum = 0; acm->cfreq[acm->nsym] = 0; for (i = acm->nsym-1; i>=0; i--) { acm->freq[i] = (acm->freq[i] + 1) / 2; cum += acm->freq[i]; acm->cfreq[i] = cum; } } acm->freq[sym] += 1; for (i=sym; i>=0; i--) acm->cfreq[i] += 1; return; } void ac_encoder_init (ac_encoder *ace, const char *fn) { if (fn) { ace->fp = fopen (fn, "wb"); /* open in binary mode */ check (!ace->fp, "arithmetic encoder could not open file"); } else { ace->fp = NULL; } ace->bits_to_go = 8; ace->low = 0; ace->high = Top_value; ace->fbits = 0; ace->buffer = 0; ace->total_bits = 0; return; } void ac_encoder_done (ac_encoder *ace) { ace->fbits += 1; if (ace->low < First_qtr) bit_plus_follow (ace, 0); else bit_plus_follow (ace, 1); if (ace->fp) putc (ace->buffer >> ace->bits_to_go, ace->fp); if (ace->fp) fclose (ace->fp); return; } void ac_decoder_init (ac_decoder *acd, const char *fn) { int i; acd->fp = fopen (fn, "rb"); /* open in binary mode */ check (!acd->fp, "arithmetic decoder could not open file"); acd->bits_to_go = 0; acd->garbage_bits = 0; acd->value = 0; for (i=1; i<=Code_value_bits; i++) { acd->value = 2*acd->value + input_bit(acd); } acd->low = 0; acd->high = Top_value; return; } void ac_decoder_done (ac_decoder *acd) { fclose (acd->fp); return; } void ac_model_init (ac_model *acm, int nsym, int *ifreq, int adapt) { int i; acm->nsym = nsym; acm->freq = (int *) (void *) calloc (nsym, sizeof (int)); check (!acm->freq, "arithmetic coder model allocation failure"); acm->cfreq = (int *) (void *) calloc (nsym+1, sizeof (int)); check (!acm->cfreq, "arithmetic coder model allocation failure"); acm->adapt = adapt; if (ifreq) { acm->cfreq[acm->nsym] = 0; for (i=acm->nsym-1; i>=0; i--) { acm->freq[i] = ifreq[i]; acm->cfreq[i] = acm->cfreq[i+1] + acm->freq[i]; } if (acm->cfreq[0] > Max_frequency) error ("arithmetic coder model max frequency exceeded"); } else { for (i=0; i<acm- rel='nofollow' onclick='return false;'>nsym; i++) { acm->freq[i] = 1; acm->cfreq[i] = acm->nsym - i; } acm->cfreq[acm->nsym] = 0; } return; } void ac_model_done (ac_model *acm) { acm->nsym = 0; free (acm->freq); acm->freq = NULL; free (acm->cfreq); acm->cfreq = NULL; return; } long ac_encoder_bits (ac_encoder *ace) { return ace->total_bits; } void ac_encode_symbol (ac_encoder *ace, ac_model *acm, int sym) { long range; check (sym<0||sym>=acm->nsym, "symbol out of range"); range = (long)(ace->high-ace->low)+1; ace->high = ace->low + (range*acm->cfreq[sym])/acm->cfreq[0]-1; ace->low = ace->low + (range*acm->cfreq[sym+1])/acm->cfreq[0]; for (;;) { if (ace->high<Half) { bit_plus_follow (ace, 0); } else if (ace->low>=Half) { bit_plus_follow (ace, 1); ace->low -= Half; ace->high -= Half; } else if (ace->low>=First_qtr && ace->high<Third_qtr) { ace->fbits += 1; ace->low -= First_qtr; ace->high -= First_qtr; } else break; ace->low = 2*ace->low; ace->high = 2*ace->high+1; } if (acm->adapt) update_model (acm, sym); return; } int ac_decode_symbol (ac_decoder *acd, ac_model *acm) { long range; int cum; int sym; range = (long)(acd->high-acd->low)+1; cum = (((long)(acd->value-acd->low)+1)*acm->cfreq[0]-1)/range; for (sym = 0; acm->cfreq[sym+1]>cum; sym++) /* do nothing */ ; check (sym<0||sym>=acm->nsym, "symbol out of range"); acd->high = acd->low + (range*acm->cfreq[sym])/acm->cfreq[0]-1; acd->low = acd->low + (range*acm->cfreq[sym+1])/acm->cfreq[0]; for (;;) { if (acd->high<Half) { /* do nothing */ } else if (acd->low>=Half) { acd->value -= Half; acd->low -= Half; acd->high -= Half; } else if (acd->low>=First_qtr && acd->high<Third_qtr) { acd->value -= First_qtr; acd->low -= First_qtr; acd->high -= First_qtr; } else break; acd->low = 2*acd->low; acd->high = 2*acd->high+1; acd->value = 2*acd->value + input_bit(acd); } if (acm->adapt) update_model (acm, sym); return sym; }