Merged Whippet into libguile/whippet

libguile/whippet/src/swar.h

@@ -0,0 +1,154 @@
+#ifndef SWAR_H
+#define SWAR_H
+
+#include <string.h>
+
+static inline size_t
+count_zero_bytes(uint64_t bytes) {
+  return bytes ? (__builtin_ctzll(bytes) / 8) : sizeof(bytes);
+}
+
+static uint64_t
+broadcast_byte(uint8_t byte) {
+  uint64_t result = byte;
+  return result * 0x0101010101010101ULL;
+}
+
+static inline uint64_t
+load_eight_aligned_bytes(uint8_t *ptr) {
+  GC_ASSERT(((uintptr_t)ptr & 7) == 0);
+  uint8_t * __attribute__((aligned(8))) aligned_ptr = ptr;
+  uint64_t word;
+  memcpy(&word, aligned_ptr, 8);
+#ifdef WORDS_BIGENDIAN
+  word = __builtin_bswap64(word);
+#endif
+  return word;
+}
+
+static inline uint64_t
+match_bytes_against_bits(uint64_t bytes, uint8_t mask) {
+  return bytes & broadcast_byte(mask);
+}
+
+static inline size_t
+scan_for_byte_with_bits(uint8_t *ptr, size_t limit, uint8_t mask) {
+  size_t n = 0;
+  size_t unaligned = ((uintptr_t) ptr) & 7;
+  if (unaligned) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr - unaligned) >> (unaligned * 8);
+    uint64_t match = match_bytes_against_bits(bytes, mask);
+    if (match)
+      return count_zero_bytes(match);
+    n += 8 - unaligned;
+  }
+
+  for(; n < limit; n += 8) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr + n);
+    uint64_t match = match_bytes_against_bits(bytes, mask);
+    if (match)
+      return n + count_zero_bytes(match);
+  }
+
+  return limit;
+}
+
+static inline uint64_t
+match_bytes_against_tag(uint64_t bytes, uint8_t mask, uint8_t tag) {
+  // Precondition: tag within mask.
+  GC_ASSERT_EQ(tag & mask, tag);
+  // Precondition: high bit of mask byte is empty, so that we can add without
+  // overflow.
+  GC_ASSERT_EQ(mask & 0x7f, mask);
+  // Precondition: mask is low bits of byte.
+  GC_ASSERT(mask);
+  GC_ASSERT_EQ(mask & (mask + 1), 0);
+
+  uint64_t vmask = broadcast_byte(mask);
+  uint64_t vtest = broadcast_byte(mask + 1);
+  uint64_t vtag = broadcast_byte(tag);
+
+  bytes &= vmask;
+  uint64_t m = (bytes ^ vtag) + vmask;
+  return (m & vtest) ^ vtest;
+}
+
+static inline size_t
+scan_for_byte_with_tag(uint8_t *ptr, size_t limit, uint8_t mask, uint8_t tag) {
+  // The way we handle unaligned reads by padding high bytes with zeroes assumes
+  // that all-zeroes is not a matching byte.
+  GC_ASSERT(tag);
+
+  size_t n = 0;
+  size_t unaligned = ((uintptr_t) ptr) & 7;
+  if (unaligned) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr - unaligned) >> (unaligned * 8);
+    uint64_t match = match_bytes_against_tag(bytes, mask, tag);
+    if (match)
+      return count_zero_bytes(match);
+    n += 8 - unaligned;
+  }
+
+  for(; n < limit; n += 8) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr + n);
+    uint64_t match = match_bytes_against_tag(bytes, mask, tag);
+    if (match)
+      return n + count_zero_bytes(match);
+  }
+
+  return limit;
+}
+
+static inline uint64_t
+match_bytes_against_2_tags(uint64_t bytes, uint8_t mask, uint8_t tag1,
+                           uint8_t tag2) 
+{
+  // Precondition: tags are covered by within mask.
+  GC_ASSERT_EQ(tag1 & mask, tag1);
+  GC_ASSERT_EQ(tag2 & mask, tag2);
+  // Precondition: high bit of mask byte is empty, so that we can add without
+  // overflow.
+  GC_ASSERT_EQ(mask & 0x7f, mask);
+  // Precondition: mask is low bits of byte.
+  GC_ASSERT(mask);
+  GC_ASSERT_EQ(mask & (mask + 1), 0);
+  
+  uint64_t vmask = broadcast_byte(mask);
+  uint64_t vtest = broadcast_byte(mask + 1);
+  uint64_t vtag1 = broadcast_byte(tag1);
+  uint64_t vtag2 = broadcast_byte(tag2);
+
+  bytes &= vmask;
+  uint64_t m1 = (bytes ^ vtag1) + vmask;
+  uint64_t m2 = (bytes ^ vtag2) + vmask;
+  return ((m1 & m2) & vtest) ^ vtest;
+}
+
+static inline size_t
+scan_for_byte_with_tags(uint8_t *ptr, size_t limit, uint8_t mask,
+                        uint8_t tag1, uint8_t tag2) {
+  // The way we handle unaligned reads by padding high bytes with zeroes assumes
+  // that all-zeroes is not a matching byte.
+  GC_ASSERT(tag1 && tag2);
+
+  size_t n = 0;
+  size_t unaligned = ((uintptr_t) ptr) & 7;
+  if (unaligned) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr - unaligned) >> (unaligned * 8);
+    uint64_t match = match_bytes_against_2_tags(bytes, mask, tag1, tag2);
+    if (match)
+      return count_zero_bytes(match);
+    n += 8 - unaligned;
+  }
+
+  for(; n < limit; n += 8) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr + n);
+    uint64_t match = match_bytes_against_2_tags(bytes, mask, tag1, tag2);
+    if (match)
+      return n + count_zero_bytes(match);
+  }
+
+  return limit;
+}
+
+#endif // SWAR_H