Microsoft Specific
Emits the Streaming SIMD Extensions 4 (SSE4) instruction pextrb. This instruction extracts an 8-bit unsigned integer from a 128-bit parameter.
int _mm_extract_epi8(
__m128i a,
const int ndx
);
Parameters
[in] a
A 128-bit parameter that contains sixteen 8-bit integers. These integers can be signed or unsigned.[in] ndx
A constant index that specifies the location of the value to extract.
Result value
The return value can be expressed by the following equation:
r := (ndx == 0) ? a0 :
((ndx == 1) ? a1 :
...
((ndx == 14) ? a14 : a15))
Requirements
Intrinsic |
Architecture |
|---|---|
_mm_extract_epi8 |
x86, x64 |
Header file <smmintrin.h>
Remarks
a0 - a15 are the individual 8-bit integers in parameter a, with a0 occupying the lowest 8 bits.
Only the least significant four bits of ndx are used.
The result is the unsigned equivalent of the appropriate 8-bits in parameter a.
Before you use this intrinsic, software must ensure that the processor supports the instruction.
Example
#include <stdio.h>
#include <smmintrin.h>
int main ()
{
__m128i a;
const int ndx1 = 4;
const int ndx2 = 13;
a.m128i_i8[0] = 1;
a.m128i_i8[1] = 2;
a.m128i_i8[2] = 4;
a.m128i_i8[3] = 8;
a.m128i_i8[4] = 16;
a.m128i_i8[5] = 32;
a.m128i_i8[6] = 64;
a.m128i_i8[7] = 127;
a.m128i_i8[8] = -1;
a.m128i_i8[9] = -2;
a.m128i_i8[10] = -4;
a.m128i_i8[11] = -8;
a.m128i_i8[12] = -16;
a.m128i_i8[13] = -32;
a.m128i_i8[14] = -64;
a.m128i_i8[15] = -128;
int res = _mm_extract_epi8(a, ndx1);
printf_s("Result res should equal %d: %d\n", a.m128i_u8[ndx1], res);
res = _mm_extract_epi8(a, ndx2);
printf_s("Result res should equal %d: %d\n", a.m128i_u8[ndx2], res);
return 0;
}
Result res should equal 16: 16 Result res should equal 224: 224