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stb_image: NEON YCbCr->RGB kernel.

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Also ran a bunch of test cases to make sure the IDCT and H2V2
resamplers were correct.
This commit is contained in:
Fabian Giesen 2014-12-24 01:38:59 +01:00
parent 7d32f74d8a
commit fd987527f1
1 changed files with 52 additions and 5 deletions
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57
stb_image.h
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@ -2829,16 +2829,15 @@ static void stbi__YCbCr_to_RGB_row(stbi_uc *out, const stbi_uc *y, const stbi_uc
}
#endif
#ifdef STBI_SSE2
static void stbi__YCbCr_to_RGB_sse2(stbi_uc *out, stbi_uc const *y, stbi_uc const *pcb, stbi_uc const *pcr, int count, int step)
#if defined(STBI_SSE2) || defined(STBI_NEON)
static void stbi__YCbCr_to_RGB_simd(stbi_uc *out, stbi_uc const *y, stbi_uc const *pcb, stbi_uc const *pcr, int count, int step)
{
int i = 0;
#ifdef STBI_SSE2
// step == 3 is pretty ugly on the final interleave, and i'm not convinced
// it's useful in practice (you wouldn't use it for textures, for example).
// so just accelerate step == 4 case.
//
// note: unlike the IDCT, this isn't bit-identical to the integer version.
if (step == 4) {
// this is a fairly straightforward implementation and not super-optimized.
__m128i signflip = _mm_set1_epi8(-0x80);
@ -2894,6 +2893,53 @@ static void stbi__YCbCr_to_RGB_sse2(stbi_uc *out, stbi_uc const *y, stbi_uc cons
out += 32;
}
}
#endif
#ifdef STBI_NEON
// in this version, step=3 support would be easy to add. but is there demand?
if (step == 4) {
// this is a fairly straightforward implementation and not super-optimized.
uint8x8_t signflip = vdup_n_u8(0x80);
int16x8_t cr_const0 = vdupq_n_s16( (short) ( 1.40200f*4096.0f+0.5f));
int16x8_t cr_const1 = vdupq_n_s16( - (short) ( 0.71414f*4096.0f+0.5f));
int16x8_t cb_const0 = vdupq_n_s16( - (short) ( 0.34414f*4096.0f+0.5f));
int16x8_t cb_const1 = vdupq_n_s16( (short) ( 1.77200f*4096.0f+0.5f));
for (; i+7 < count; i += 8) {
// load
uint8x8_t y_bytes = vld1_u8(y + i);
uint8x8_t cr_bytes = vld1_u8(pcr + i);
uint8x8_t cb_bytes = vld1_u8(pcb + i);
int8x8_t cr_biased = vreinterpret_s8_u8(vsub_u8(cr_bytes, signflip));
int8x8_t cb_biased = vreinterpret_s8_u8(vsub_u8(cb_bytes, signflip));
// expand to s16
int16x8_t yws = vreinterpretq_s16_u16(vshll_n_u8(y_bytes, 4));
int16x8_t crw = vshll_n_s8(cr_biased, 7);
int16x8_t cbw = vshll_n_s8(cb_biased, 7);
// color transform
int16x8_t cr0 = vqdmulhq_s16(crw, cr_const0);
int16x8_t cb0 = vqdmulhq_s16(cbw, cb_const0);
int16x8_t cr1 = vqdmulhq_s16(crw, cr_const1);
int16x8_t cb1 = vqdmulhq_s16(cbw, cb_const1);
int16x8_t rws = vaddq_s16(yws, cr0);
int16x8_t gws = vaddq_s16(vaddq_s16(yws, cb0), cr1);
int16x8_t bws = vaddq_s16(yws, cb1);
// undo scaling, round, convert to byte
uint8x8x4_t o;
o.val[0] = vqrshrun_n_s16(rws, 4);
o.val[1] = vqrshrun_n_s16(gws, 4);
o.val[2] = vqrshrun_n_s16(bws, 4);
o.val[3] = vdup_n_u8(255);
// store, interleaving r/g/b/a
vst4_u8(out, o);
out += 8*4;
}
}
#endif
for (; i < count; ++i) {
int y_fixed = (y[i] << 20) + (1<<19); // rounding
@ -2929,7 +2975,7 @@ static void stbi__setup_jpeg(stbi__jpeg *j)
if (stbi__sse2_available()) {
j->idct_block_kernel = stbi__idct_sse2;
#ifndef STBI_JPEG_OLD
j->YCbCr_to_RGB_kernel = stbi__YCbCr_to_RGB_sse2;
j->YCbCr_to_RGB_kernel = stbi__YCbCr_to_RGB_simd;
#endif
j->resample_row_hv_2_kernel = stbi__resample_row_hv_2_simd;
}
@ -2937,6 +2983,7 @@ static void stbi__setup_jpeg(stbi__jpeg *j)
#ifdef STBI_NEON
j->idct_block_kernel = stbi__idct_neon;
j->YCbCr_to_RGB_kernel = stbi__YCbCr_to_RGB_simd;
j->resample_row_hv_2_kernel = stbi__resample_row_hv_2_simd;
#endif
}