cosmopolitan/libc/intrin/phsubsw.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
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│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
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│ PERFORMANCE OF THIS SOFTWARE.                                                │
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#include "libc/intrin/phsubsw.h"
#include "libc/limits.h"
#include "libc/macros.internal.h"

/**
 * Subtracts adjacent shorts w/ saturation.
 *
 * @param 𝑎 [w/o] receives reduced 𝑏 and 𝑐 concatenated
 * @param 𝑏 [r/o] supplies four pairs of shorts
 * @param 𝑐 [r/o] supplies four pairs of shorts
 * @note goes fast w/ ssse3 (intel c. 2004, amd c. 2011)
 * @mayalias
 */
void(phsubsw)(int16_t a[8], const int16_t b[8], const int16_t c[8]) {
  int i, t[8];
  t[0] = b[0] - b[1];
  t[1] = b[2] - b[3];
  t[2] = b[4] - b[5];
  t[3] = b[6] - b[7];
  t[4] = c[0] - c[1];
  t[5] = c[2] - c[3];
  t[6] = c[4] - c[5];
  t[7] = c[6] - c[7];
  for (i = 0; i < 8; ++i) {
    a[i] = MIN(SHRT_MAX, MAX(SHRT_MIN, t[i]));
  }
}