On Thu, Feb 18, 2016 at 11:36:18AM +0100, Clément Bœsch wrote: > Hi, > > While working on PNG DSP, I realized the filter up was doing extra > overflow checks on the bytes non multiple of the long word size. This > logic is present in both C and x86 ASM. Here is the current C code for > reference: > > -------------- 8< ---------------- > > // 0x7f7f7f7f or 0x7f7f7f7f7f7f7f7f or whatever, depending on the cpu's > native arithmetic size > #define pb_7f (~0UL / 255 * 0x7f) > #define pb_80 (~0UL / 255 * 0x80) > > static void add_bytes_l2_c(uint8_t *dst, uint8_t *src1, uint8_t *src2, int w) > { > long i; > for (i = 0; i <= w - (int) sizeof(long); i += sizeof(long)) { > long a = *(long *)(src1 + i); > long b = *(long *)(src2 + i); > *(long *)(dst + i) = ((a & pb_7f) + (b & pb_7f)) ^ ((a ^ b) & pb_80); > } > for (; i < w; i++) > dst[i] = src1[i] + src2[i]; > } > > -------------- 8< ---------------- > > The thing is, the buffers seem to be 0 padded to 16 (see > av_fast_padded_malloc() calls). I'm assuming there are cases where it's > not?
isnt dst the AVFrame in one call ? so that this would write over width if it wrote beyond ? [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB No great genius has ever existed without some touch of madness. -- Aristotle
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