Revert "Speed up tail processing when hashing aligned C strings"

This reverts commit 07f0f6abfc7f6c55cede528d9689dedecefc734a.

This has shown failures on both Valgrind and big-endian machines,
per members skink and pike.

diff --git a/src/include/common/hashfn_unstable.h b/src/include/common/hashfn_unstable.h
index bd7323fe052bd18f33c6ecadc4c5c618bfe9668e..791750d136c48b4818a1c3f41b4681fa52b45b14 100644 (file)
--- a/src/include/common/hashfn_unstable.h
+++ b/src/include/common/hashfn_unstable.h
@@ -219,9 +219,8 @@ static inline size_t
 fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
 {
        const char *const start = str;
-       uint64          chunk;
+       size_t          remainder;
        uint64          zero_byte_low;
-       uint64          mask;
 
        Assert(PointerIsAligned(start, uint64));
 
@@ -240,7 +239,7 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
         */
        for (;;)
        {
-               chunk = *(uint64 *) str;
+               uint64          chunk = *(uint64 *) str;
 
 #ifdef WORDS_BIGENDIAN
                zero_byte_low = haszero64(pg_bswap64(chunk));
@@ -255,37 +254,14 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
                str += FH_SIZEOF_ACCUM;
        }
 
-       if (zero_byte_low & 0xFF)
-       {
-               /*
-                * The next byte in the input is the NUL terminator, so we have
-                * nothing to do.
-                */
-       }
-       else
-       {
-               /*
-                * Create a mask for the remaining bytes so we can combine them into
-                * the hash. The mask also covers the NUL terminator, but that's
-                * harmless. The mask could contain 0x80 in bytes corresponding to the
-                * input past the terminator, but only where the input byte is zero or
-                * one, so also harmless.
-                */
-               mask = zero_byte_low | (zero_byte_low - 1);
-#ifdef WORDS_BIGENDIAN
-               /* need to mask the upper bytes */
-               mask = pg_bswap64(mask);
-#endif
-               hs->accum = chunk & mask;
-               fasthash_combine(hs);
-
-               /*
-                * The byte corresponding to the NUL will be 0x80, so the rightmost
-                * bit position will be in the range 15, 23, ..., 63. Turn this into
-                * byte position by dividing by 8.
-                */
-               str += pg_rightmost_one_pos64(zero_byte_low) / BITS_PER_BYTE;
-       }
+       /*
+        * The byte corresponding to the NUL will be 0x80, so the rightmost bit
+        * position will be in the range 7, 15, ..., 63. Turn this into byte
+        * position by dividing by 8.
+        */
+       remainder = pg_rightmost_one_pos64(zero_byte_low) / BITS_PER_BYTE;
+       fasthash_accum(hs, str, remainder);
+       str += remainder;
 
        return str - start;
 }