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rescaler: better handling of the fxy_scale=0 special case.

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Change-Id: I635cb62c028e373a54fcafdc6b996812a9b2ace5
This commit is contained in:
Pascal Massimino 2015-10-06 00:15:18 -07:00 committed by James Zern
parent 55c05293d5
commit 6dfa5e3e58
1 changed files with 10 additions and 3 deletions
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13
src/utils/rescaler.c
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@ -48,9 +48,16 @@ void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
wrk->y_sub = wrk->y_expand ? y_sub - 1 : y_sub;
wrk->y_accum = wrk->y_expand ? wrk->y_sub : wrk->y_add;
if (!wrk->y_expand) {
// note the very special case where x_add = y_add = 1 cannot be represented.
// We special-case fxy_scale = 0 in this case, in WebPRescalerExportRow().
wrk->fxy_scale = WEBP_RESCALER_FRAC(dst_height, wrk->x_add * wrk->y_add);
// this is WEBP_RESCALER_FRAC(dst_height, x_add * y_add) without the cast.
const uint64_t ratio =
(uint64_t)dst_height * WEBP_RESCALER_ONE / (wrk->x_add * wrk->y_add);
if (ratio != (uint32_t)ratio) {
// We can't represent the ratio with the current fixed-point precision.
// => We special-case fxy_scale = 0, in WebPRescalerExportRow().
wrk->fxy_scale = 0;
} else {
wrk->fxy_scale = (uint32_t)ratio;
}
wrk->fy_scale = WEBP_RESCALER_FRAC(1, wrk->y_sub);
} else {
wrk->fy_scale = WEBP_RESCALER_FRAC(1, wrk->x_add);