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我試圖重寫一些代碼以利用SSE。然而,由於某些原因,我的SSE版本產生了與原始版本不同的結果,例如, 209.1而不是1.47等。與SSE版本不同的結果
爲什麼?整個功能可以找到here。
struct vec_ps
{
__m128 value;
vec_ps(){}
vec_ps(float value) : value(_mm_set1_ps(value)) {}
vec_ps(__m128 value) : value(value) {}
vec_ps(const vec_ps& other) : value(other.value) {}
vec_ps& operator=(const vec_ps& other)
{
value = other.value;
return *this;
}
vec_ps& operator+=(const vec_ps& other)
{
value = _mm_add_ps(value, other.value);
return *this;
}
vec_ps& operator-=(const vec_ps& other)
{
value = _mm_sub_ps(value, other.value);
return *this;
}
vec_ps& operator*=(const vec_ps& other)
{
value = _mm_mul_ps(value, other.value);
return *this;
}
vec_ps& operator/=(const vec_ps& other)
{
value = _mm_div_ps(value, other.value);
return *this;
}
static vec_ps load(float* ptr)
{
return vec_ps(_mm_load_ps(ptr));
}
static void stream(float* ptr, const vec_ps& other)
{
_mm_stream_ps(ptr, other.value);
}
void stream(float* ptr)
{
_mm_stream_ps(ptr, value);
}
};
vec_ps operator+(const vec_ps& lhs, const vec_ps& rhs)
{
return vec_ps(lhs) += rhs;
}
vec_ps operator-(const vec_ps& lhs, const vec_ps& rhs)
{
return vec_ps(lhs) -= rhs;
}
vec_ps operator*(const vec_ps& lhs, const vec_ps& rhs)
{
return vec_ps(lhs) *= rhs;
}
vec_ps operator/(const vec_ps& lhs, const vec_ps& rhs)
{
return vec_ps(lhs) /= rhs;
}
void foo(/*...*/)
{
std::vector<float, tbb::cache_aligned_allocator<float>> ref_mu(w*h);
std::vector<float, tbb::cache_aligned_allocator<float>> cmp_mu(w*h);
std::vector<float, tbb::cache_aligned_allocator<float>> ref_sigma_sqd(w*h);
std::vector<float, tbb::cache_aligned_allocator<float>> cmp_sigma_sqd(w*h);
std::vector<float, tbb::cache_aligned_allocator<float>> sigma_both(w*h);
int size = w*h*sizeof(float);
/*...*/
float ssim_sum = 0.0;
float ssim_sum2 = 0.0;
vec_ps ssim_sum_ps(0.0f);
for(int n = 0; n < size/16; ++n)
{
auto ref_mu_ps = vec_ps::load(ref_mu.data() + n*4);
auto cmp_mu_ps = vec_ps::load(cmp_mu.data() + n*4);
auto sigma_both_ps = vec_ps::load(sigma_both.data() + n*4);
auto ref_sigma_sqd_ps = vec_ps::load(ref_sigma_sqd.data() + n*4);
auto cmp_sigma_sqd_ps = vec_ps::load(cmp_sigma_sqd.data() + n*4);
auto numerator = (2.0f * ref_mu_ps * cmp_mu_ps + C1) * (2.0f * sigma_both_ps + C2);
auto denominator = (ref_mu_ps*ref_mu_ps + cmp_mu_ps*cmp_mu_ps + C1) * (ref_sigma_sqd_ps + cmp_sigma_sqd_ps + C2);
ssim_sum_ps += numerator/denominator;
}
for(int n = 0; n < 4; ++n)
ssim_sum2 += ssim_sum_ps.value.m128_f32[n];
for (int y = 0; y < h; ++y)
{
int offset = y*w;
for (int x = 0; x < w; ++x, ++offset)
{
float numerator = (2.0f * ref_mu[offset] * cmp_mu[offset] + C1) * (2.0f * sigma_both[offset] + C2);
float denominator = (ref_mu[offset]*ref_mu[offset] + cmp_mu[offset]*cmp_mu[offset] + C1) * (ref_sigma_sqd[offset] + cmp_sigma_sqd[offset] + C2);
ssim_sum += numerator/denominator;
}
}
assert(ssim_sum2 == ssim_sum); // FAILS!
}
你可以也應該自己調試。在調試器中運行它,或添加printf調用以輸出中間結果。當你隔離不按預期工作的步驟時,請隨時編寫一個最小的測試用例並在此處詢問。但是「這裏是一堆代碼,弄清楚什麼是錯誤的」不是一個好問題。 – 2012-01-15 02:04:16
@ BenVoigt; Ofc,你是對的。不過,我已經習慣了在發佈之前所建議的內容,而無法弄清楚。 – ronag 2012-01-15 02:12:47
那麼,哪一行代碼會產生「錯誤」的結果呢?你可以刪除TBB分配器等,並簡化一些事情嗎? – 2012-01-15 02:14:46