我正在尝试找到一种用于 RGB8 到 RGB32 图像转换的程序集优化方法。
源是 8 位灰度图像，目标应该是 32 位灰度图像 (BGRA)，第 4 通道 (alpha) 被忽略。源地址不保证 16 字节对齐，Count 是 16 的倍数，目标地址是 16 字节对齐。
- 输入：8位单通道灰度图像
- 输出：32 位 BGRA（忽略 alpha 通道）
- COUNT：图像大小是 16 的倍数
- CPU：x86-32（允许 SSE2/SSE3）
这是我优化的汇编代码。有没有更快的转换方式？
void ConvertGreyToRgb32Assembler(__m128i* Source, __m128i* Destination, unsigned int Count) {
static unsigned int __declspec(align(64)) Masks[] = {
0x80000000, 0x80010101, 0x80020202, 0x80030303,
0x80040404, 0x80050505, 0x80060606, 0x80070707,
0x80080808, 0x80090909, 0x800a0a0a, 0x800b0b0b,
0x800c0c0c, 0x800d0d0d, 0x800e0e0e, 0x800f0f0f
};
__asm {
mov esi, Source
mov edi, Destination
mov edx, Count
xor ecx, ecx
movdqa xmm4, xmmword ptr [Masks + 0]
movdqa xmm5, xmmword ptr [Masks + 16]
movdqa xmm6, xmmword ptr [Masks + 32]
movdqa xmm7, xmmword ptr [Masks + 48]
l1:
movdqu xmm0, xmmword ptr [esi + ecx]
movdqa xmm1, xmm0
movdqa xmm2, xmm0
movdqa xmm3, xmm0
pshufb xmm0, xmm4
pshufb xmm1, xmm5
pshufb xmm2, xmm6
pshufb xmm3, xmm7
movntdq [edi + 0], xmm0
movntdq [edi + 16], xmm1
movntdq [edi + 32], xmm2
movntdq [edi + 48], xmm3
add edi, 64
add ecx, 16
cmp ecx, edx
jb l1
}
}
还有另一种使用几个 PUNPCKLBW 和 PUNPCKHBW 的方法，但这似乎有点慢。
更新：这是基本的非优化算法：
BGRA* Destination = ...
unsigned char* Source ...
for (unsigned int i = 0; i < Size; i++) {
Destination[i].Blue = Source[i];
Destination[i].Green = Source[i];
Destination[i].Red = Source[i];
}
PS：我还尝试将 C 代码与 MS VS2008 SSE 编译器内在函数一起使用。事实证明，编译器产生了大量不必要的内存移动，导致代码比纯汇编慢 10-20%。
更新 2：这是仅使用内部函数的相同代码。
void ConvertGreyToRgb32Assembler(__m128i* Source, __m128i* Destination, unsigned int Count) {
static const unsigned int __declspec(align(64)) Masks[] = {
0x80000000, 0x80010101, 0x80020202, 0x80030303,
0x80040404, 0x80050505, 0x80060606, 0x80070707,
0x80080808, 0x80090909, 0x800a0a0a, 0x800b0b0b,
0x800c0c0c, 0x800d0d0d, 0x800e0e0e, 0x800f0f0f
};
register __m128i m0 = _mm_load_si128((__m128i*) (Masks + 0));
register __m128i m1 = _mm_load_si128((__m128i*) (Masks + 4));
register __m128i m2 = _mm_load_si128((__m128i*) (Masks + 8));
register __m128i m3 = _mm_load_si128((__m128i*) (Masks + 12));
for (unsigned int i = 0; i < Count / 16; i++) {
__m128i r0 = _mm_load_si128(Source + i);
_mm_stream_si128(Destination + (i * 4) + 0, _mm_shuffle_epi8(r0, m0));
_mm_stream_si128(Destination + (i * 4) + 1, _mm_shuffle_epi8(r0, m1));
_mm_stream_si128(Destination + (i * 4) + 2, _mm_shuffle_epi8(r0, m2));
_mm_stream_si128(Destination + (i * 4) + 3, _mm_shuffle_epi8(r0, m3));
}
}
更新3：这是编译器生成的代码（美化）（Visual Studio 2012，所有优化）：
push ebp
mov ebp, esp
mov edx, dword ptr [ebp+8]
movdqa xmm1, xmmword ptr ds:[Masks + 0]
movdqa xmm2, xmmword ptr ds:[Masks + 16]
movdqa xmm3, xmmword ptr ds:[Masks + 32]
movdqa xmm4, xmmword ptr ds:[Masks + 48]
push esi
test ecx, ecx
je l2
lea esi, [ecx-1]
shr esi, 4
inc esi
l1:
mov ecx, edx
movdqu xmm0, xmmword ptr [ecx]
mov ecx, eax
movdqa xmm5, xmm0
pshufb xmm5, xmm1
movdqa xmmword ptr [ecx], xmm5
movdqa xmm5, xmm0
pshufb xmm5, xmm2
movdqa xmmword ptr [eax+10h], xmm5
movdqa xmm5, xmm0
pshufb xmm5, xmm3
movdqa xmmword ptr [eax+20h], xmm5
lea ecx, [eax+30h]
add edx, 10h
add eax, 40h
dec esi
pshufb xmm0, xmm4
movdqa xmmword ptr [ecx], xmm0
jne l1
l2:
pop esi
pop ebp
ret
似乎交错movdqa与pshufb更快一些。
更新 4：这似乎是最佳的手动优化代码：
__asm {
mov esi, Source
mov edi, Destination
mov ecx, Count
movdqu xmm0, xmmword ptr [esi]
movdqa xmm4, xmmword ptr [Masks + 0]
movdqa xmm5, xmmword ptr [Masks + 16]
movdqa xmm6, xmmword ptr [Masks + 32]
movdqa xmm7, xmmword ptr [Masks + 48]
l1:
dec ecx
lea edi, [ edi + 64 ]
lea esi, [ esi + 16 ]
movdqa xmm1, xmm0
movdqa xmm2, xmm0
movdqa xmm3, xmm0
pshufb xmm0, xmm4
movdqa [edi - 64], xmm0
pshufb xmm1, xmm5
movdqa [edi - 48], xmm1
pshufb xmm2, xmm6
movdqa [edi - 32], xmm2
pshufb xmm3, xmm7
movdqa [edi - 16], xmm3
movdqu xmm0, xmmword ptr [esi]
ja l1
}
更新 5：此转换算法使用punpck指令。但是，此转换例程比使用掩码和pushfb.
for (unsigned int i = 0; i < Count; i += 16) {
register __m128i r0 = _mm_load_si128(Source++);
register __m128i r1 = _mm_unpackhi_epi8(r0, r0);
register __m128i r2 = _mm_unpacklo_epi8(r0, r0);
register __m128i r3 = _mm_unpackhi_epi8(r1, r1);
register __m128i r4 = _mm_unpacklo_epi8(r1, r1);
register __m128i r5 = _mm_unpackhi_epi8(r2, r2);
register __m128i r6 = _mm_unpacklo_epi8(r2, r2);
_mm_store_si128(Destination++, r6);
_mm_store_si128(Destination++, r5);
_mm_store_si128(Destination++, r4);
_mm_store_si128(Destination++, r3);
}
更新 6：为了完整起见，这是从 32 位转换回 8 位灰度图像的逆方法。
static void ConvertRgb32ToGrey(const __m128i* Source, __m128i* Destination, unsigned int Count) {
static const unsigned char __declspec(align(64)) Masks[] = {
0x00, 0x04, 0x08, 0x0c, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
0x80, 0x80, 0x80, 0x80, 0x00, 0x04, 0x08, 0x0c, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x00, 0x04, 0x08, 0x0c, 0x80, 0x80, 0x80, 0x80,
0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x00, 0x04, 0x08, 0x0c,
};
register __m128i m0 = _mm_load_si128((__m128i*) (Masks + 0));
register __m128i m1 = _mm_load_si128((__m128i*) (Masks + 16));
register __m128i m2 = _mm_load_si128((__m128i*) (Masks + 32));
register __m128i m3 = _mm_load_si128((__m128i*) (Masks + 48));
for (unsigned int i = 0; i < Count / 64; i++) {
__m128i a = _mm_load_si128(Source + (i * 4) + 0);
__m128i b = _mm_load_si128(Source + (i * 4) + 1);
__m128i c = _mm_load_si128(Source + (i * 4) + 2);
__m128i d = _mm_load_si128(Source + (i * 4) + 3);
a = _mm_shuffle_epi8(a, m0);
b = _mm_shuffle_epi8(b, m1);
c = _mm_shuffle_epi8(c, m2);
d = _mm_shuffle_epi8(d, m3);
__m128i e = _mm_or_si128(a, b);
__m128i f = _mm_or_si128(c, d);
__m128i g = _mm_or_si128(e, f);
_mm_stream_si128(Destination + i, g);
}
}