C 快速计数_m128i寄存器中的设置位数
我应该计算uum128i寄存器的设置位数。 特别是,我应该使用以下方法编写两个能够计算寄存器位数的函数C 快速计数_m128i寄存器中的设置位数,c,sse,simd,sse2,hammingweight,C,Sse,Simd,Sse2,Hammingweight,我应该计算uum128i寄存器的设置位数。 特别是,我应该使用以下方法编写两个能够计算寄存器位数的函数 寄存器的设置位总数 寄存器每个字节的设置位数 是否存在可以全部或部分执行上述操作的内在函数?编辑:我想我不明白OP在寻找什么,但我会保留我的答案,以防它对遇到此问题的其他人有用 C提供了一些不错的按位操作 下面是计算整数中设置的位数的代码: countBitsSet(int toCount) { int numBitsSet = 0; while(toCount != 0)
是否存在可以全部或部分执行上述操作的内在函数?编辑:我想我不明白OP在寻找什么,但我会保留我的答案,以防它对遇到此问题的其他人有用 C提供了一些不错的按位操作 下面是计算整数中设置的位数的代码:
countBitsSet(int toCount)
{
int numBitsSet = 0;
while(toCount != 0)
{
count += toCount % 2;
toCount = toCount >> 1;
}
return numBitsSet;
}
说明:
toCount % 2
返回整数中的最后一位。(除以2并检查余数)。我们将其添加到总计数中,然后将toCount值的位移位1。应继续此操作,直到toCount中没有设置更多位为止(当toCount等于0时)
要计算特定字节中的位数,您需要使用掩码。以下是一个例子:
countBitsInByte(int toCount, int byteNumber)
{
int mask = 0x000F << byteNumber * 8
return countBitsSet(toCount & mask)
}
countBitsInByte(int-toCount,int-byteNumber)
{
int mask=0x000F以下是我在旧项目()中使用的一些代码。下面的函数popcnt8
计算每个字节中设置的位数
仅SSE2版本(基于中的算法3):
SSSE3版本(到期):
XOP版本(相当于SSSE3,但使用AMD推土机上更快的XOP指令)
下面的函数popcnt64
统计SSE寄存器的低位和高位64位部分的位数:
static inline int popcnt128(__m128i n) {
const __m128i cnt64 = popcnt64(n);
const __m128i cnt64_hi = _mm_unpackhi_epi64(cnt64, cnt64);
const __m128i cnt128 = _mm_add_epi32(cnt64, cnt64_hi);
return _mm_cvtsi128_si32(cnt128);
}
SSE2版本:
static inline __m128i popcnt64(__m128i n) {
const __m128i cnt8 = popcnt8(n);
return _mm_sad_epu8(cnt8, _mm_setzero_si128());
}
XOP版本:
static inline __m128i popcnt64(__m128i n) {
const __m128i cnt8 = popcnt8(n);
return _mm_haddq_epi8(cnt8);
}
最后,下面的函数popcnt128
计算整个128位寄存器中的位数:
static inline int popcnt128(__m128i n) {
const __m128i cnt64 = popcnt64(n);
const __m128i cnt64_hi = _mm_unpackhi_epi64(cnt64, cnt64);
const __m128i cnt128 = _mm_add_epi32(cnt64, cnt64_hi);
return _mm_cvtsi128_si32(cnt128);
}
但是,实现popcnt128
的更有效方法是使用硬件POPCNT指令(在支持它的处理器上):
正如第一条评论中所说,gcc 3.4+提供了一个方便的访问(希望是最佳的)内置via的途径
int __builtin_popcount (unsigned int x) /* Returns the number of 1-bits in x. */
如下文所述:
并没有准确地回答128位的问题,但很好地回答了我在这里登陆时遇到的问题:)这是一个基于的版本,命名类似于其他内在函数,以及一些额外的16、32和64位向量函数
#include "immintrin.h"
/* bit masks: 0x55 = 01010101, 0x33 = 00110011, 0x0f = 00001111 */
static const __m128i m1 = {0x5555555555555555ULL,0x5555555555555555ULL};
static const __m128i m2 = {0x3333333333333333ULL,0x3333333333333333ULL};
static const __m128i m3 = {0x0f0f0f0f0f0f0f0fULL,0x0f0f0f0f0f0f0f0fULL};
static const __m128i m4 = {0x001f001f001f001fULL,0x001f001f001f001fULL};
static const __m128i m5 = {0x0000003f0000003fULL,0x0000003f0000003fULL};
__m128i _mm_popcnt_epi8(__m128i x) {
/* Note: if we returned x here it would be like _mm_popcnt_epi1(x) */
__m128i y;
/* add even and odd bits*/
y = _mm_srli_epi64(x,1); //put even bits in odd place
y = _mm_and_si128(y,m1); //mask out the even bits (0x55)
x = _mm_subs_epu8(x,y); //shortcut to mask even bits and add
/* if we just returned x here it would be like _mm_popcnt_epi2(x) */
/* now add the half nibbles */
y = _mm_srli_epi64 (x,2); //move half nibbles in place to add
y = _mm_and_si128(y,m2); //mask off the extra half nibbles (0x0f)
x = _mm_and_si128(x,m2); //ditto
x = _mm_adds_epu8(x,y); //totals are a maximum of 5 bits (0x1f)
/* if we just returned x here it would be like _mm_popcnt_epi4(x) */
/* now add the nibbles */
y = _mm_srli_epi64(x,4); //move nibbles in place to add
x = _mm_adds_epu8(x,y); //totals are a maximum of 6 bits (0x3f)
x = _mm_and_si128(x,m3); //mask off the extra bits
return x;
}
__m128i _mm_popcnt_epi16(__m128i x) {
__m128i y;
x = _mm_popcnt_epi8(x); //get byte popcount
y = _mm_srli_si128(x,1); //copy even bytes for adding
x = _mm_add_epi16(x,y); //add even bytes into the odd bytes
return _mm_and_si128(x,m4);//mask off the even byte and return
}
__m128i _mm_popcnt_epi32(__m128i x) {
__m128i y;
x = _mm_popcnt_epi16(x); //get word popcount
y = _mm_srli_si128(x,2); //copy even words for adding
x = _mm_add_epi32(x,y); //add even words into odd words
return _mm_and_si128(x,m5);//mask off the even words and return
}
__m128i _mm_popcnt_epi64(__m128i x){
/* _mm_sad_epu8() is weird
It takes the absolute difference of bytes between 2 __m128i
then horizontal adds the lower and upper 8 differences
and stores the sums in the lower and upper 64 bits
*/
return _mm_sad_epu8(_mm_popcnt_epi8(x),(__m128i){0});
}
int _mm_popcnt_si128(__m128i x){
x = _mm_popcnt_epi64(x);
__m128i y = _mm_srli_si128(x,8);
return _mm_add_epi64(x,y)[0];
//alternative: __builtin_popcntll(x[0])+__builtin_popcntll(x[1]);
}
最近的CPU有一条POPCNT
(填充计数)指令;GCC通过内置的方式将其公开。请参阅,了解更多信息。MS也有popcount函数…请参阅…注意,这些函数不一定比bithack快;如果在数组中计算位,则一些bithack函数会稍微快一些。有内置函数(映射到CPU指令的内部函数,如POPCNT
),问题是如何计算128位SSE(XMM)中的设置位注册,不是一个int
。啊,我知道我没有完全理解这个问题。如果合适的话,我会编辑我的回答并保持它,以防有人无意中发现。C不提供“nice”按位运算。你甚至不能移植得到算术右移!实现可以是2的补码,但有符号类型上的>
可以是逻辑移位。但实际上,人们真正想要使用的所有编译器都给你符号类型上的算术右移,因此你的函数是一个infinite循环负数toCount
。有符号的%2
比&1
需要更多的工作,因为它必须为负数奇数生成-1
。但是(在普通编译器上)如果toCount
为负数,则您的函数永远不会返回,因此问题被隐藏了……似乎您是上述研究论文的共同作者之一:-)剪贴工作人员的总结也很好。你的解决方案是最新的。哈克姆的把戏不再是最新的了。太好了,伙计!哦,太糟糕了。你在ACM上发表了你的论文,所以不幸的是,我不付15美元就看不懂了:-(@NilsPipenbrinck,论文可在会议网站上免费获得:conferences.computer.org/sc/2012/papers/1000a033.pdfappa事实上,你的SSE2版本通常比SSSE3版本快。SSSE3的指令更少并不重要。这里有一个基准:@Soonts它可能是,但单凭Microsoft编译器的结果并不矛盾vincing。为什么第一步之后的步骤需要饱和adds
而不是常规的add
(尽管根据Agner Fog的指令表,paddusb
在所有方面都与paddb
具有相同的性能,因此没有性能理由避免饱和add。这只是令人惊讶。)
static inline int popcnt128(__m128i n) {
const __m128i n_hi = _mm_unpackhi_epi64(n, n);
#ifdef _MSC_VER
return __popcnt64(_mm_cvtsi128_si64(n)) + __popcnt64(_mm_cvtsi128_si64(n_hi));
#else
return __popcntq(_mm_cvtsi128_si64(n)) + __popcntq(_mm_cvtsi128_si64(n_hi));
#endif
}
int __builtin_popcount (unsigned int x) /* Returns the number of 1-bits in x. */
#include "immintrin.h"
/* bit masks: 0x55 = 01010101, 0x33 = 00110011, 0x0f = 00001111 */
static const __m128i m1 = {0x5555555555555555ULL,0x5555555555555555ULL};
static const __m128i m2 = {0x3333333333333333ULL,0x3333333333333333ULL};
static const __m128i m3 = {0x0f0f0f0f0f0f0f0fULL,0x0f0f0f0f0f0f0f0fULL};
static const __m128i m4 = {0x001f001f001f001fULL,0x001f001f001f001fULL};
static const __m128i m5 = {0x0000003f0000003fULL,0x0000003f0000003fULL};
__m128i _mm_popcnt_epi8(__m128i x) {
/* Note: if we returned x here it would be like _mm_popcnt_epi1(x) */
__m128i y;
/* add even and odd bits*/
y = _mm_srli_epi64(x,1); //put even bits in odd place
y = _mm_and_si128(y,m1); //mask out the even bits (0x55)
x = _mm_subs_epu8(x,y); //shortcut to mask even bits and add
/* if we just returned x here it would be like _mm_popcnt_epi2(x) */
/* now add the half nibbles */
y = _mm_srli_epi64 (x,2); //move half nibbles in place to add
y = _mm_and_si128(y,m2); //mask off the extra half nibbles (0x0f)
x = _mm_and_si128(x,m2); //ditto
x = _mm_adds_epu8(x,y); //totals are a maximum of 5 bits (0x1f)
/* if we just returned x here it would be like _mm_popcnt_epi4(x) */
/* now add the nibbles */
y = _mm_srli_epi64(x,4); //move nibbles in place to add
x = _mm_adds_epu8(x,y); //totals are a maximum of 6 bits (0x3f)
x = _mm_and_si128(x,m3); //mask off the extra bits
return x;
}
__m128i _mm_popcnt_epi16(__m128i x) {
__m128i y;
x = _mm_popcnt_epi8(x); //get byte popcount
y = _mm_srli_si128(x,1); //copy even bytes for adding
x = _mm_add_epi16(x,y); //add even bytes into the odd bytes
return _mm_and_si128(x,m4);//mask off the even byte and return
}
__m128i _mm_popcnt_epi32(__m128i x) {
__m128i y;
x = _mm_popcnt_epi16(x); //get word popcount
y = _mm_srli_si128(x,2); //copy even words for adding
x = _mm_add_epi32(x,y); //add even words into odd words
return _mm_and_si128(x,m5);//mask off the even words and return
}
__m128i _mm_popcnt_epi64(__m128i x){
/* _mm_sad_epu8() is weird
It takes the absolute difference of bytes between 2 __m128i
then horizontal adds the lower and upper 8 differences
and stores the sums in the lower and upper 64 bits
*/
return _mm_sad_epu8(_mm_popcnt_epi8(x),(__m128i){0});
}
int _mm_popcnt_si128(__m128i x){
x = _mm_popcnt_epi64(x);
__m128i y = _mm_srli_si128(x,8);
return _mm_add_epi64(x,y)[0];
//alternative: __builtin_popcntll(x[0])+__builtin_popcntll(x[1]);
}