Initial import

libc/intrin/pmaddubsw.c

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+/*-*- 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│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/pmaddubsw.h"
+#include "libc/limits.h"
+#include "libc/macros.h"
+
+/**
+ * Multiplies bytes and adds adjacent results w/ short saturation.
+ *
+ *     𝑤ᵢ ← CLAMP[ 𝑏₂ᵢ𝑐₂ᵢ + 𝑏₍₂ᵢ₊₁₎𝑐₍₂ᵢ₊₁₎ ]
+ *
+ * @param 𝑤 [w/o] receives shorts
+ * @param 𝑏 [r/o] is your byte data
+ * @param 𝑐 [r/o] are your int8 coefficients
+ * @note SSSE3 w/ Prescott c. 2004, Bulldozer c. 2011
+ * @note greatest simd op, like, ever
+ * @mayalias
+ */
+void(pmaddubsw)(short w[8], const unsigned char b[16],
+                const signed char c[16]) {
+  int i;
+  for (i = 0; i < 8; ++i) {
+    w[i] = MIN(SHRT_MAX, MAX(SHRT_MIN, (c[i * 2 + 0] * b[i * 2 + 0] +
+                                        c[i * 2 + 1] * b[i * 2 + 1])));
+  }
+}