我正在紧密循环中实现双线性插值,并尝试使用SSE优化它,但我没有从中得到任何加速。
这是代码,非SIMD版本使用一个简单的向量结构,可以定义为
重新排列汇编代码以重复使用寄存器(最终只使用了三个xmm寄存器)没有产生任何效果。我还尝试使用内部函数:
而且没有任何效果。我是否漏掉了什么,或者在这里获得额外的速度是不可能的?
这是代码,非SIMD版本使用一个简单的向量结构,可以定义为
struct Vec3f { float x,y,z; }
,并实现了乘法和加法运算符:#ifdef USE_SIMD
const Color c11 = pixelCache[y1 * size.x + x1];
const Color c12 = pixelCache[y2 * size.x + x1];
const Color c22 = pixelCache[y2 * size.x + x2];
const Color c21 = pixelCache[y1 * size.x + x2];
__declspec(align(16)) float mc11[4] = { 1.0, c11.GetB(), c11.GetG(), c11.GetR() };
__declspec(align(16)) float mc12[4] = { 1.0, c12.GetB(), c12.GetG(), c12.GetR() };
__declspec(align(16)) float mc22[4] = { 1.0, c22.GetB(), c22.GetG(), c22.GetR() };
__declspec(align(16)) float mc21[4] = { 1.0, c21.GetB(), c21.GetG(), c21.GetR() };
// scalars in vector form for SSE
const float s11 = (x2-x)*(y2-y);
const float s12 = (x2-x)*(y-y1);
const float s22 = (x-x1)*(y-y1);
const float s21 = (x-x1)*(y2-y);
__declspec(align(16)) float ms11[4] = {1.0, s11, s11, s11};
__declspec(align(16)) float ms12[4] = {1.0, s12, s12, s12};
__declspec(align(16)) float ms22[4] = {1.0, s22, s22, s22};
__declspec(align(16)) float ms21[4] = {1.0, s21, s21, s21};
__asm {
movaps xmm0, mc11
movaps xmm1, mc12
movaps xmm2, mc22
movaps xmm3, mc21
movaps xmm4, ms11
movaps xmm5, ms12
movaps xmm6, ms22
movaps xmm7, ms21
mulps xmm0, xmm4
mulps xmm1, xmm5
mulps xmm2, xmm6
mulps xmm3, xmm7
addps xmm0, xmm1
addps xmm0, xmm2
addps xmm0, xmm3
movaps mc11, xmm0
}
#else
const Vec3f c11 = toFloat(pixelCache[y1 * size.x + x1]);
const Vec3f c12 = toFloat(pixelCache[y2 * size.x + x1]);
const Vec3f c22 = toFloat(pixelCache[y2 * size.x + x2]);
const Vec3f c21 = toFloat(pixelCache[y1 * size.x + x2]);
const Vec3f colour =
c11*(x2-x)*(y2-y) +
c21*(x-x1)*(y2-y) +
c12*(x2-x)*(y-y1) +
c22*(x-x1)*(y-y1);
#endif
重新排列汇编代码以重复使用寄存器(最终只使用了三个xmm寄存器)没有产生任何效果。我还尝试使用内部函数:
// perform bilinear interpolation
const Vec3f c11 = toFloat(pixelCache[y1 * size.x + x1]);
const Vec3f c12 = toFloat(pixelCache[y2 * size.x + x1]);
const Vec3f c22 = toFloat(pixelCache[y2 * size.x + x2]);
const Vec3f c21 = toFloat(pixelCache[y1 * size.x + x2]);
// scalars in vector form for SSE
const float s11 = (x2-x)*(y2-y);
const float s12 = (x2-x)*(y-y1);
const float s22 = (x-x1)*(y-y1);
const float s21 = (x-x1)*(y2-y);
__m128 mc11 = _mm_set_ps(1.f, c11.b, c11.g, c11.r);
__m128 mc12 = _mm_set_ps(1.f, c12.b, c12.g, c12.r);
__m128 mc22 = _mm_set_ps(1.f, c22.b, c22.g, c22.r);
__m128 mc21 = _mm_set_ps(1.f, c21.b, c21.g, c21.r);
__m128 ms11 = _mm_set_ps(1.f, s11, s11, s11);
__m128 ms12 = _mm_set_ps(1.f, s12, s12, s12);
__m128 ms22 = _mm_set_ps(1.f, s22, s22, s22);
__m128 ms21 = _mm_set_ps(1.f, s21, s21, s21);
mc11 = _mm_mul_ps(mc11, ms11);
mc12 = _mm_mul_ps(mc12, ms12);
mc22 = _mm_mul_ps(mc22, ms22);
mc21 = _mm_mul_ps(mc21, ms21);
mc11 = _mm_add_ps(mc11, mc12);
mc11 = _mm_add_ps(mc11, mc22);
mc11 = _mm_add_ps(mc11, mc21);
Vec3f colour;
_mm_storeu_ps(colour.array, mc11);
而且没有任何效果。我是否漏掉了什么,或者在这里获得额外的速度是不可能的?