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speed-up MapToPalette() with binary search

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goes from ~2% CPU to ~0.7% for large images
Change-Id: Ibd8a0fde9ba553f93157a49dcb7da0426209e404
This commit is contained in:
Pascal Massimino 2016-05-23 15:39:54 +02:00
parent 576362abd7
commit fdd29a3d3f
1 changed files with 39 additions and 13 deletions
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52
src/enc/vp8l.c
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@ -1192,8 +1192,35 @@ static WebPEncodingError MakeInputImageCopy(VP8LEncoder* const enc) {
// -----------------------------------------------------------------------------
static void MapToPalette(const uint32_t palette[], int num_colors,
static int SearchColor(const uint32_t sorted[], uint32_t color, int hi) {
int low = 0;
if (sorted[low] == color) return low; // loop invariant: sorted[low] != color
while (1) {
const int mid = (low + hi) >> 1;
if (sorted[mid] == color) {
return mid;
} else if (sorted[mid] < color) {
low = mid;
} else {
hi = mid;
}
}
}
// Sort palette in increasing order and prepare an inverse mapping array.
static void PrepareMapToPalette(const uint32_t palette[], int num_colors,
uint32_t sorted[], int idx_map[]) {
int i;
memcpy(sorted, palette, num_colors * sizeof(*sorted));
qsort(sorted, num_colors, sizeof(*sorted), PaletteCompareColorsForQsort);
for (i = 0; i < num_colors; ++i) {
idx_map[SearchColor(sorted, palette[i], num_colors)] = i;
}
}
static void MapToPalette(const uint32_t sorted_palette[], int num_colors,
uint32_t* const last_pix, int* const last_idx,
const int idx_map[],
const uint32_t* src, uint8_t* dst, int width) {
int x;
int prev_idx = *last_idx;
@ -1201,14 +1228,8 @@ static void MapToPalette(const uint32_t palette[], int num_colors,
for (x = 0; x < width; ++x) {
const uint32_t pix = src[x];
if (pix != prev_pix) {
int i;
for (i = 0; i < num_colors; ++i) {
if (pix == palette[i]) {
prev_idx = i;
prev_pix = pix;
break;
}
}
prev_idx = idx_map[SearchColor(sorted_palette, pix, num_colors)];
prev_pix = pix;
}
dst[x] = prev_idx;
}
@ -1255,11 +1276,16 @@ static WebPEncodingError ApplyPalette(const uint32_t* src, uint32_t src_stride,
}
} else {
// Use 1 pixel cache for ARGB pixels.
uint32_t last_pix = palette[0];
int last_idx = 0;
uint32_t last_pix;
int last_idx;
uint32_t sorted[MAX_PALETTE_SIZE];
int idx_map[MAX_PALETTE_SIZE];
PrepareMapToPalette(palette, palette_size, sorted, idx_map);
last_pix = palette[0];
last_idx = 0;
for (y = 0; y < height; ++y) {
MapToPalette(palette, palette_size, &last_pix, &last_idx,
src, tmp_row, width);
MapToPalette(sorted, palette_size, &last_pix, &last_idx,
idx_map, src, tmp_row, width);
VP8LBundleColorMap(tmp_row, width, xbits, dst);
src += src_stride;
dst += dst_stride;