NEON implementation for Adler32

third_party/zlib/neon_adler32.c

+/* Copyright 2017 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+*/
+
+#include "neon_adler32.h"
+#ifdef __ARM_NEON__
+#include <arm_neon.h>
+
+static void NEON_accum32(uint32_t *s, const unsigned char *buf,
+                         unsigned int len)
+{
+  static const uint8_t taps[32] = {
+    32, 31, 30, 29, 28, 27, 26, 25,
+    24, 23, 22, 21, 20, 19, 18, 17,
+    16, 15, 14, 13, 12, 11, 10, 9,
+    8, 7, 6, 5, 4, 3, 2, 1 };
+
+  uint8x16_t t0 = vld1q_u8(taps), t1 = vld1q_u8(taps + 16);
+
+  uint32x4_t adacc = vdupq_n_u32(0), s2acc = vdupq_n_u32(0);
+  adacc = vsetq_lane_u32(s[0], adacc, 0);
+  s2acc = vsetq_lane_u32(s[1], s2acc, 0);
+
+  while (len >= 2) {
+    uint8x16_t d0 = vld1q_u8(buf), d1 = vld1q_u8(buf + 16);
+    uint16x8_t adler, sum2;
+    s2acc = vaddq_u32(s2acc, vshlq_n_u32(adacc, 5));
+    adler = vpaddlq_u8(       d0);
+    adler = vpadalq_u8(adler, d1);
+    sum2 = vmull_u8(      vget_low_u8(t0), vget_low_u8(d0));
+    sum2 = vmlal_u8(sum2, vget_high_u8(t0), vget_high_u8(d0));
+    sum2 = vmlal_u8(sum2, vget_low_u8(t1), vget_low_u8(d1));
+    sum2 = vmlal_u8(sum2, vget_high_u8(t1), vget_high_u8(d1));
+    adacc = vpadalq_u16(adacc, adler);
+    s2acc = vpadalq_u16(s2acc, sum2);
+    len -= 2;
+    buf += 32;
+  }
+
+
+  while (len > 0) {
+    uint8x16_t d0 = vld1q_u8(buf);
+    uint16x8_t adler, sum2;
+    s2acc = vaddq_u32(s2acc, vshlq_n_u32(adacc, 4));
+    adler = vpaddlq_u8(d0);
+    sum2 = vmull_u8(      vget_low_u8(t1), vget_low_u8(d0));
+    sum2 = vmlal_u8(sum2, vget_high_u8(t1), vget_high_u8(d0));
+    adacc = vpadalq_u16(adacc, adler);
+    s2acc = vpadalq_u16(s2acc, sum2);
+    buf += 16;
+    len--;
+  }
+
+  {
+    uint32x2_t adacc2 = vpadd_u32(vget_low_u32(adacc), vget_high_u32(adacc));
+    uint32x2_t s2acc2 = vpadd_u32(vget_low_u32(s2acc), vget_high_u32(s2acc));
+    uint32x2_t as = vpadd_u32(adacc2, s2acc2);
+    s[0] = vget_lane_u32(as, 0);
+    s[1] = vget_lane_u32(as, 1);
+  }
+}
+
+static void NEON_handle_tail(uint32_t *pair, const unsigned char *buf,
+                             unsigned int len)
+{
+  /* Oldie K&R code integration. */
+  unsigned int i;
+  for (i = 0; i < len; ++i) {
+    pair[0] += buf[i];
+    pair[1] += pair[0];
+  }
+}
+
+unsigned long NEON_adler32(unsigned long adler, const unsigned char *buf,
+                           const unsigned int len)
+{
+  /* The largest prime smaller than 65536. */
+  const uint32_t M_BASE = 65521;
+  /* This is the threshold where doing accumulation may overflow. */
+  const int M_NMAX = 5552;
+
+  unsigned long sum2;
+  uint32_t pair[2];
+  int n = M_NMAX;
+  unsigned int done = 0;
+  /* Oldie K&R code integration. */
+  unsigned int i;
+
+  /* Split Adler-32 into component sums, it can be supplied by
+   * the caller sites (e.g. in a PNG file).
+   */
+  sum2 = (adler >> 16) & 0xffff;
+  adler &= 0xffff;
+  pair[0] = adler;
+  pair[1] = sum2;
+
+  for (i = 0; i < len; i += n) {
+    if (i + n > len)

[cavalcantii1, 2017/02/04 18:53:01]

Add parenthesis i.e. if ((i + n) > len)

+      n = len - i;
+
+    if (n < 16)
+      break;
+
+    NEON_accum32(pair, buf + i, n / 16);
+    pair[0] %= M_BASE;
+    pair[1] %= M_BASE;
+
+    done += (n / 16) * 16;
+  }
+
+  /* Handle the tail elements. */
+  if (done < len) {
+    NEON_handle_tail(pair, (buf + done), len - done);
+    pair[0] %= M_BASE;
+    pair[1] %= M_BASE;
+  }
+
+  /* D = B * 65536 + A, see: https://en.wikipedia.org/wiki/Adler-32. */
+  return (pair[1] << 16) | pair[0];
+}
+#endif