Factor nofl-space out of whippet

src/swar.h

@@ -0,0 +1,51 @@
+#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 size_t
+scan_for_byte(uint8_t *ptr, size_t limit, uint64_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);
+    bytes &= mask;
+    if (bytes)
+      return count_zero_bytes(bytes);
+    n += 8 - unaligned;
+  }
+
+  for(; n < limit; n += 8) {
+    uint64_t bytes = load_eight_aligned_bytes(ptr + n);
+    bytes &= mask;
+    if (bytes)
+      return n + count_zero_bytes(bytes);
+  }
+
+  return limit;
+}
+
+#endif // SWAR_H