diff options
Diffstat (limited to 'jdhuff.c')
| -rw-r--r-- | jdhuff.c | 126 |
1 files changed, 69 insertions, 57 deletions
@@ -71,13 +71,24 @@ typedef struct { d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; /* Whether we care about the DC and AC coefficient values for each block */ - boolean dc_needed[D_MAX_BLOCKS_IN_MCU]; - boolean ac_needed[D_MAX_BLOCKS_IN_MCU]; + int coef_limit[D_MAX_BLOCKS_IN_MCU]; } huff_entropy_decoder; typedef huff_entropy_decoder * huff_entropy_ptr; +static const int jpeg_zigzag_order[DCTSIZE2] = { + 0, 1, 5, 6, 14, 15, 27, 28, + 2, 4, 7, 13, 16, 26, 29, 42, + 3, 8, 12, 17, 25, 30, 41, 43, + 9, 11, 18, 24, 31, 40, 44, 53, + 10, 19, 23, 32, 39, 45, 52, 54, + 20, 22, 33, 38, 46, 51, 55, 60, + 21, 34, 37, 47, 50, 56, 59, 61, + 35, 36, 48, 49, 57, 58, 62, 63 +}; + + /* * Initialize for a Huffman-compressed scan. */ @@ -86,7 +97,7 @@ METHODDEF(void) start_pass_huff_decoder (j_decompress_ptr cinfo) { huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; - int ci, blkn, dctbl, actbl; + int ci, blkn, dctbl, actbl, i; jpeg_component_info * compptr; /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. @@ -120,11 +131,13 @@ start_pass_huff_decoder (j_decompress_ptr cinfo) entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; /* Decide whether we really care about the coefficient values */ if (compptr->component_needed) { - entropy->dc_needed[blkn] = TRUE; - /* we don't need the ACs if producing a 1/8th-size image */ - entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1); + ci = compptr->DCT_v_scaled_size; + if (ci <= 0 || ci > 8) ci = 8; + i = compptr->DCT_h_scaled_size; + if (i <= 0 || i > 8) i = 8; + entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[(ci - 1) * DCTSIZE + i - 1]; } else { - entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; + entropy->coef_limit[blkn] = 0; } } @@ -435,26 +448,20 @@ jpeg_huff_decode (bitread_working_state * state, /* * Figure F.12: extend sign bit. - * On some machines, a shift and add will be faster than a table lookup. + * On some machines, a shift and sub will be faster than a table lookup. */ #ifdef AVOID_TABLES -#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) +#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x)) #else -#define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) +#define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x)) -static const int extend_test[16] = /* entry n is 2**(n-1) */ - { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, - 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; - -static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ - { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, - ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, - ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, - ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; +static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */ + { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, + 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF }; #endif /* AVOID_TABLES */ @@ -541,39 +548,40 @@ decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { JBLOCKROW block = MCU_data[blkn]; - d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; - d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; + d_derived_tbl * htbl; register int s, k, r; + int coef_limit, ci; /* Decode a single block's worth of coefficients */ /* Section F.2.2.1: decode the DC coefficient difference */ - HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); - if (s) { - CHECK_BIT_BUFFER(br_state, s, return FALSE); - r = GET_BITS(s); - s = HUFF_EXTEND(r, s); - } + htbl = entropy->dc_cur_tbls[blkn]; + HUFF_DECODE(s, br_state, htbl, return FALSE, label1); - if (entropy->dc_needed[blkn]) { + htbl = entropy->ac_cur_tbls[blkn]; + k = 1; + coef_limit = entropy->coef_limit[blkn]; + if (coef_limit) { /* Convert DC difference to actual value, update last_dc_val */ - int ci = cinfo->MCU_membership[blkn]; + if (s) { + CHECK_BIT_BUFFER(br_state, s, return FALSE); + r = GET_BITS(s); + s = HUFF_EXTEND(r, s); + } + ci = cinfo->MCU_membership[blkn]; s += state.last_dc_val[ci]; state.last_dc_val[ci] = s; - /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ + /* Output the DC coefficient */ (*block)[0] = (JCOEF) s; - } - - if (entropy->ac_needed[blkn]) { /* Section F.2.2.2: decode the AC coefficients */ /* Since zeroes are skipped, output area must be cleared beforehand */ - for (k = 1; k < DCTSIZE2; k++) { - HUFF_DECODE(s, br_state, actbl, return FALSE, label2); - + for (; k < coef_limit; k++) { + HUFF_DECODE(s, br_state, htbl, return FALSE, label2); + r = s >> 4; s &= 15; - + if (s) { k += r; CHECK_BIT_BUFFER(br_state, s, return FALSE); @@ -586,33 +594,37 @@ decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) (*block)[jpeg_natural_order[k]] = (JCOEF) s; } else { if (r != 15) - break; + goto EndOfBlock; k += 15; } } - } else { - - /* Section F.2.2.2: decode the AC coefficients */ - /* In this path we just discard the values */ - for (k = 1; k < DCTSIZE2; k++) { - HUFF_DECODE(s, br_state, actbl, return FALSE, label3); - - r = s >> 4; - s &= 15; - - if (s) { - k += r; - CHECK_BIT_BUFFER(br_state, s, return FALSE); - DROP_BITS(s); - } else { - if (r != 15) - break; - k += 15; - } + if (s) { + CHECK_BIT_BUFFER(br_state, s, return FALSE); + DROP_BITS(s); } + } + + /* Section F.2.2.2: decode the AC coefficients */ + /* In this path we just discard the values */ + for (; k < DCTSIZE2; k++) { + HUFF_DECODE(s, br_state, htbl, return FALSE, label3); + + r = s >> 4; + s &= 15; + if (s) { + k += r; + CHECK_BIT_BUFFER(br_state, s, return FALSE); + DROP_BITS(s); + } else { + if (r != 15) + break; + k += 15; + } } + + EndOfBlock: ; } /* Completed MCU, so update state */ |