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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.
pull/62/head
Fabian Giesen 2014-12-14 01:23:42 -08:00
parent 1d5652044d
commit 518306517c
1 changed files with 29 additions and 27 deletions
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56
stb_image.h
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@ -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;