From 518306517c4b5b0e7d7077781ac974828fb907a1 Mon Sep 17 00:00:00 2001 From: Fabian Giesen Date: Sun, 14 Dec 2014 01:23:42 -0800 Subject: [PATCH] stb_image: JPEG dequant in decode_block not IDCT. Inside decode_block, we're still sparse, and we can use that sparsity pattern without doing extra work to discover it. --- stb_image.h | 56 +++++++++++++++++++++++++++++--------------------------- 1 file changed, 29 insertions(+), 27 deletions(-) diff --git a/stb_image.h b/stb_image.h index 832393d..ed804c3 100644 --- a/stb_image.h +++ b/stb_image.h @@ -1007,9 +1007,6 @@ typedef struct typedef struct { - #ifdef STBI_SIMD - unsigned short dequant2[4][64]; - #endif stbi__context *s; stbi__huffman huff_dc[4]; stbi__huffman huff_ac[4]; @@ -1220,7 +1217,7 @@ static stbi_uc stbi__jpeg_dezigzag[64+15] = }; // decode one 64-entry block-- -static int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64], stbi__huffman *hdc, stbi__huffman *hac, stbi__int16 *fac, int b) +static int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64], stbi__huffman *hdc, stbi__huffman *hac, stbi__int16 *fac, int b, stbi_uc *dequant) { int diff,dc,k; int t; @@ -1235,11 +1232,12 @@ static int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64], stbi__huffman diff = t ? stbi__extend_receive(j, t) : 0; dc = j->img_comp[b].dc_pred + diff; j->img_comp[b].dc_pred = dc; - data[0] = (short) dc; + data[0] = (short) (dc * dequant[0]); // decode AC components, see JPEG spec k = 1; do { + unsigned int zig; int c,r,s; if (j->code_bits < 16) stbi__grow_buffer_unsafe(j); c = (j->code_buffer >> (32 - FAST_BITS)) & ((1 << FAST_BITS)-1); @@ -1250,7 +1248,8 @@ static int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64], stbi__huffman j->code_buffer <<= s; j->code_bits -= s; // decode into unzigzag'd location - data[stbi__jpeg_dezigzag[k++]] = (short) (r >> 8); + zig = stbi__jpeg_dezigzag[k++]; + data[zig] = (short) ((r >> 8) * dequant[zig]); } else { int rs = stbi__jpeg_huff_decode(j, hac); if (rs < 0) return stbi__err("bad huffman code","Corrupt JPEG"); @@ -1262,7 +1261,8 @@ static int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64], stbi__huffman } else { k += r; // decode into unzigzag'd location - data[stbi__jpeg_dezigzag[k++]] = (short) stbi__extend_receive(j,s); + zig = stbi__jpeg_dezigzag[k++]; + data[zig] = (short) (stbi__extend_receive(j,s) * dequant[zig]); } } } while (k < 64); @@ -1322,21 +1322,23 @@ stbi_inline static stbi_uc stbi__clamp(int x) t0 += p1+p3; #ifdef STBI_SIMD -typedef unsigned short stbi_dequantize_t; -#else -typedef stbi_uc stbi_dequantize_t; +static unsigned short stbi__dq_ones[64] = { + 1,1,1,1, 1,1,1,1, 1,1,1,1, 1,1,1,1, + 1,1,1,1, 1,1,1,1, 1,1,1,1, 1,1,1,1, + 1,1,1,1, 1,1,1,1, 1,1,1,1, 1,1,1,1, + 1,1,1,1, 1,1,1,1, 1,1,1,1, 1,1,1,1, +}; #endif // .344 seconds on 3*anemones.jpg -static void stbi__idct_block(stbi_uc *out, int out_stride, short data[64], stbi_dequantize_t *dequantize) +static void stbi__idct_block(stbi_uc *out, int out_stride, short data[64]) { int i,val[64],*v=val; - stbi_dequantize_t *dq = dequantize; stbi_uc *o; short *d = data; // columns - for (i=0; i < 8; ++i,++d,++dq, ++v) { + for (i=0; i < 8; ++i,++d, ++v) { // if all zeroes, shortcut -- this avoids dequantizing 0s and IDCTing if (d[ 8]==0 && d[16]==0 && d[24]==0 && d[32]==0 && d[40]==0 && d[48]==0 && d[56]==0) { @@ -1344,11 +1346,10 @@ static void stbi__idct_block(stbi_uc *out, int out_stride, short data[64], stbi_ // (1|2|3|4|5|6|7)==0 0 seconds // all separate -0.047 seconds // 1 && 2|3 && 4|5 && 6|7: -0.047 seconds - int dcterm = d[0] * dq[0] << 2; + int dcterm = d[0] << 2; v[0] = v[8] = v[16] = v[24] = v[32] = v[40] = v[48] = v[56] = dcterm; } else { - STBI__IDCT_1D(d[ 0]*dq[ 0],d[ 8]*dq[ 8],d[16]*dq[16],d[24]*dq[24], - d[32]*dq[32],d[40]*dq[40],d[48]*dq[48],d[56]*dq[56]) + STBI__IDCT_1D(d[ 0],d[ 8],d[16],d[24],d[32],d[40],d[48],d[56]) // constants scaled things up by 1<<12; let's bring them back // down, but keep 2 extra bits of precision x0 += 512; x1 += 512; x2 += 512; x3 += 512; @@ -1390,7 +1391,12 @@ static void stbi__idct_block(stbi_uc *out, int out_stride, short data[64], stbi_ } #ifdef STBI_SIMD -static stbi_idct_8x8 stbi__idct_installed = stbi__idct_block; +static void stbi__idct_block_wrapper(stbi_uc *out, int out_stride, short data[64], unsigned short dequant[64]) +{ + stbi__idct_block(out, out_stride, data); +} + +static stbi_idct_8x8 stbi__idct_installed = stbi__idct_block_wrapper; STBIDEF void stbi_install_idct(stbi_idct_8x8 func) { @@ -1450,11 +1456,11 @@ static int stbi__parse_entropy_coded_data(stbi__jpeg *z) for (j=0; j < h; ++j) { for (i=0; i < w; ++i) { int ha = z->img_comp[n].ha; - if (!stbi__jpeg_decode_block(z, data, z->huff_dc+z->img_comp[n].hd, z->huff_ac+ha, z->fast_ac[ha], n)) return 0; + if (!stbi__jpeg_decode_block(z, data, z->huff_dc+z->img_comp[n].hd, z->huff_ac+ha, z->fast_ac[ha], n, z->dequant[z->img_comp[n].tq])) return 0; #ifdef STBI_SIMD - stbi__idct_installed(z->img_comp[n].data+z->img_comp[n].w2*j*8+i*8, z->img_comp[n].w2, data, z->dequant2[z->img_comp[n].tq]); + stbi__idct_installed(z->img_comp[n].data+z->img_comp[n].w2*j*8+i*8, z->img_comp[n].w2, data, stbi__dq_ones); #else - stbi__idct_block(z->img_comp[n].data+z->img_comp[n].w2*j*8+i*8, z->img_comp[n].w2, data, z->dequant[z->img_comp[n].tq]); + stbi__idct_block(z->img_comp[n].data+z->img_comp[n].w2*j*8+i*8, z->img_comp[n].w2, data); #endif // every data block is an MCU, so countdown the restart interval if (--z->todo <= 0) { @@ -1481,11 +1487,11 @@ static int stbi__parse_entropy_coded_data(stbi__jpeg *z) int x2 = (i*z->img_comp[n].h + x)*8; int y2 = (j*z->img_comp[n].v + y)*8; int ha = z->img_comp[n].ha; - if (!stbi__jpeg_decode_block(z, data, z->huff_dc+z->img_comp[n].hd, z->huff_ac+ha, z->fast_ac[ha], n)) return 0; + if (!stbi__jpeg_decode_block(z, data, z->huff_dc+z->img_comp[n].hd, z->huff_ac+ha, z->fast_ac[ha], n, z->dequant[z->img_comp[n].tq])) return 0; #ifdef STBI_SIMD - stbi__idct_installed(z->img_comp[n].data+z->img_comp[n].w2*y2+x2, z->img_comp[n].w2, data, z->dequant2[z->img_comp[n].tq]); + stbi__idct_installed(z->img_comp[n].data+z->img_comp[n].w2*y2+x2, z->img_comp[n].w2, data, stbi__dq_ones); #else - stbi__idct_block(z->img_comp[n].data+z->img_comp[n].w2*y2+x2, z->img_comp[n].w2, data, z->dequant[z->img_comp[n].tq]); + stbi__idct_block(z->img_comp[n].data+z->img_comp[n].w2*y2+x2, z->img_comp[n].w2, data); #endif } } @@ -1530,10 +1536,6 @@ static int stbi__process_marker(stbi__jpeg *z, int m) if (t > 3) return stbi__err("bad DQT table","Corrupt JPEG"); for (i=0; i < 64; ++i) z->dequant[t][stbi__jpeg_dezigzag[i]] = stbi__get8(z->s); - #ifdef STBI_SIMD - for (i=0; i < 64; ++i) - z->dequant2[t][i] = z->dequant[t][i]; - #endif L -= 65; } return L==0;