__lasx_xvfrstpi_b

LASX intrinsic · group: Misc

Synopsis

__m256i __lasx_xvfrstpi_b (__m256i a, __m256i b, imm0_31 imm)
#include <lasxintrin.h>
Instruction: xvfrstpi.b xr, xr, imm
CPU Flags: LASX

Description

For each 128-bit lane, find the first negative 8-bit element in b. Write its index into the lane of a selected by imm modulo 16, or write the maximum valid index plus one if no such element exists. Other elements of a remain unchanged.

Operation

for (int i = 0; i < 32; i++) {
  dst.byte[i] = a.byte[i];
}
int i;
for (i = 0; i < 16; i++) {
  if ((s8)b.byte[i] < 0) {
    break;
  }
}
dst.byte[imm % 16] = i;
for (i = 16; i < 32; i++) {
  if ((s8)b.byte[i] < 0) {
    break;
  }
}
dst.byte[(imm % 16) + 16] = i - 16;

Tested on real machine.

Latency and Throughput

CPU	µarch	Latency	Throughput (IPC)
3C5000	LA464	2	2
3A6000	LA664	2	2
3C6000	LA664	2	2

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