in Extended/libwebp/src/dsp/enc_sse2.c [29:194]
static void ITransform_SSE2(const uint8_t* ref, const int16_t* in, uint8_t* dst,
int do_two) {
// This implementation makes use of 16-bit fixed point versions of two
// multiply constants:
// K1 = sqrt(2) * cos (pi/8) ~= 85627 / 2^16
// K2 = sqrt(2) * sin (pi/8) ~= 35468 / 2^16
//
// To be able to use signed 16-bit integers, we use the following trick to
// have constants within range:
// - Associated constants are obtained by subtracting the 16-bit fixed point
// version of one:
// k = K - (1 << 16) => K = k + (1 << 16)
// K1 = 85267 => k1 = 20091
// K2 = 35468 => k2 = -30068
// - The multiplication of a variable by a constant become the sum of the
// variable and the multiplication of that variable by the associated
// constant:
// (x * K) >> 16 = (x * (k + (1 << 16))) >> 16 = ((x * k ) >> 16) + x
const __m128i k1 = _mm_set1_epi16(20091);
const __m128i k2 = _mm_set1_epi16(-30068);
__m128i T0, T1, T2, T3;
// Load and concatenate the transform coefficients (we'll do two inverse
// transforms in parallel). In the case of only one inverse transform, the
// second half of the vectors will just contain random value we'll never
// use nor store.
__m128i in0, in1, in2, in3;
{
in0 = _mm_loadl_epi64((const __m128i*)&in[0]);
in1 = _mm_loadl_epi64((const __m128i*)&in[4]);
in2 = _mm_loadl_epi64((const __m128i*)&in[8]);
in3 = _mm_loadl_epi64((const __m128i*)&in[12]);
// a00 a10 a20 a30 x x x x
// a01 a11 a21 a31 x x x x
// a02 a12 a22 a32 x x x x
// a03 a13 a23 a33 x x x x
if (do_two) {
const __m128i inB0 = _mm_loadl_epi64((const __m128i*)&in[16]);
const __m128i inB1 = _mm_loadl_epi64((const __m128i*)&in[20]);
const __m128i inB2 = _mm_loadl_epi64((const __m128i*)&in[24]);
const __m128i inB3 = _mm_loadl_epi64((const __m128i*)&in[28]);
in0 = _mm_unpacklo_epi64(in0, inB0);
in1 = _mm_unpacklo_epi64(in1, inB1);
in2 = _mm_unpacklo_epi64(in2, inB2);
in3 = _mm_unpacklo_epi64(in3, inB3);
// a00 a10 a20 a30 b00 b10 b20 b30
// a01 a11 a21 a31 b01 b11 b21 b31
// a02 a12 a22 a32 b02 b12 b22 b32
// a03 a13 a23 a33 b03 b13 b23 b33
}
}
// Vertical pass and subsequent transpose.
{
// First pass, c and d calculations are longer because of the "trick"
// multiplications.
const __m128i a = _mm_add_epi16(in0, in2);
const __m128i b = _mm_sub_epi16(in0, in2);
// c = MUL(in1, K2) - MUL(in3, K1) = MUL(in1, k2) - MUL(in3, k1) + in1 - in3
const __m128i c1 = _mm_mulhi_epi16(in1, k2);
const __m128i c2 = _mm_mulhi_epi16(in3, k1);
const __m128i c3 = _mm_sub_epi16(in1, in3);
const __m128i c4 = _mm_sub_epi16(c1, c2);
const __m128i c = _mm_add_epi16(c3, c4);
// d = MUL(in1, K1) + MUL(in3, K2) = MUL(in1, k1) + MUL(in3, k2) + in1 + in3
const __m128i d1 = _mm_mulhi_epi16(in1, k1);
const __m128i d2 = _mm_mulhi_epi16(in3, k2);
const __m128i d3 = _mm_add_epi16(in1, in3);
const __m128i d4 = _mm_add_epi16(d1, d2);
const __m128i d = _mm_add_epi16(d3, d4);
// Second pass.
const __m128i tmp0 = _mm_add_epi16(a, d);
const __m128i tmp1 = _mm_add_epi16(b, c);
const __m128i tmp2 = _mm_sub_epi16(b, c);
const __m128i tmp3 = _mm_sub_epi16(a, d);
// Transpose the two 4x4.
VP8Transpose_2_4x4_16b(&tmp0, &tmp1, &tmp2, &tmp3, &T0, &T1, &T2, &T3);
}
// Horizontal pass and subsequent transpose.
{
// First pass, c and d calculations are longer because of the "trick"
// multiplications.
const __m128i four = _mm_set1_epi16(4);
const __m128i dc = _mm_add_epi16(T0, four);
const __m128i a = _mm_add_epi16(dc, T2);
const __m128i b = _mm_sub_epi16(dc, T2);
// c = MUL(T1, K2) - MUL(T3, K1) = MUL(T1, k2) - MUL(T3, k1) + T1 - T3
const __m128i c1 = _mm_mulhi_epi16(T1, k2);
const __m128i c2 = _mm_mulhi_epi16(T3, k1);
const __m128i c3 = _mm_sub_epi16(T1, T3);
const __m128i c4 = _mm_sub_epi16(c1, c2);
const __m128i c = _mm_add_epi16(c3, c4);
// d = MUL(T1, K1) + MUL(T3, K2) = MUL(T1, k1) + MUL(T3, k2) + T1 + T3
const __m128i d1 = _mm_mulhi_epi16(T1, k1);
const __m128i d2 = _mm_mulhi_epi16(T3, k2);
const __m128i d3 = _mm_add_epi16(T1, T3);
const __m128i d4 = _mm_add_epi16(d1, d2);
const __m128i d = _mm_add_epi16(d3, d4);
// Second pass.
const __m128i tmp0 = _mm_add_epi16(a, d);
const __m128i tmp1 = _mm_add_epi16(b, c);
const __m128i tmp2 = _mm_sub_epi16(b, c);
const __m128i tmp3 = _mm_sub_epi16(a, d);
const __m128i shifted0 = _mm_srai_epi16(tmp0, 3);
const __m128i shifted1 = _mm_srai_epi16(tmp1, 3);
const __m128i shifted2 = _mm_srai_epi16(tmp2, 3);
const __m128i shifted3 = _mm_srai_epi16(tmp3, 3);
// Transpose the two 4x4.
VP8Transpose_2_4x4_16b(&shifted0, &shifted1, &shifted2, &shifted3, &T0, &T1,
&T2, &T3);
}
// Add inverse transform to 'ref' and store.
{
const __m128i zero = _mm_setzero_si128();
// Load the reference(s).
__m128i ref0, ref1, ref2, ref3;
if (do_two) {
// Load eight bytes/pixels per line.
ref0 = _mm_loadl_epi64((const __m128i*)&ref[0 * BPS]);
ref1 = _mm_loadl_epi64((const __m128i*)&ref[1 * BPS]);
ref2 = _mm_loadl_epi64((const __m128i*)&ref[2 * BPS]);
ref3 = _mm_loadl_epi64((const __m128i*)&ref[3 * BPS]);
} else {
// Load four bytes/pixels per line.
ref0 = _mm_cvtsi32_si128(WebPMemToUint32(&ref[0 * BPS]));
ref1 = _mm_cvtsi32_si128(WebPMemToUint32(&ref[1 * BPS]));
ref2 = _mm_cvtsi32_si128(WebPMemToUint32(&ref[2 * BPS]));
ref3 = _mm_cvtsi32_si128(WebPMemToUint32(&ref[3 * BPS]));
}
// Convert to 16b.
ref0 = _mm_unpacklo_epi8(ref0, zero);
ref1 = _mm_unpacklo_epi8(ref1, zero);
ref2 = _mm_unpacklo_epi8(ref2, zero);
ref3 = _mm_unpacklo_epi8(ref3, zero);
// Add the inverse transform(s).
ref0 = _mm_add_epi16(ref0, T0);
ref1 = _mm_add_epi16(ref1, T1);
ref2 = _mm_add_epi16(ref2, T2);
ref3 = _mm_add_epi16(ref3, T3);
// Unsigned saturate to 8b.
ref0 = _mm_packus_epi16(ref0, ref0);
ref1 = _mm_packus_epi16(ref1, ref1);
ref2 = _mm_packus_epi16(ref2, ref2);
ref3 = _mm_packus_epi16(ref3, ref3);
// Store the results.
if (do_two) {
// Store eight bytes/pixels per line.
_mm_storel_epi64((__m128i*)&dst[0 * BPS], ref0);
_mm_storel_epi64((__m128i*)&dst[1 * BPS], ref1);
_mm_storel_epi64((__m128i*)&dst[2 * BPS], ref2);
_mm_storel_epi64((__m128i*)&dst[3 * BPS], ref3);
} else {
// Store four bytes/pixels per line.
WebPUint32ToMem(&dst[0 * BPS], _mm_cvtsi128_si32(ref0));
WebPUint32ToMem(&dst[1 * BPS], _mm_cvtsi128_si32(ref1));
WebPUint32ToMem(&dst[2 * BPS], _mm_cvtsi128_si32(ref2));
WebPUint32ToMem(&dst[3 * BPS], _mm_cvtsi128_si32(ref3));
}
}
}