From fb51913a6c76a5d5aa09a8ef843e16cd3c383f37 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Tue, 24 Jan 2023 20:39:55 +0700
Subject: [PATCH v3 3/3] Add new symbols for reducing repetition

---
 src/include/port/pg_bitutils.h | 72 +++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 32 deletions(-)

diff --git a/src/include/port/pg_bitutils.h b/src/include/port/pg_bitutils.h
index ce04f4ffad..68aba3e090 100644
--- a/src/include/port/pg_bitutils.h
+++ b/src/include/port/pg_bitutils.h
@@ -21,6 +21,10 @@ extern PGDLLIMPORT const uint8 pg_leftmost_one_pos[256];
 extern PGDLLIMPORT const uint8 pg_rightmost_one_pos[256];
 extern PGDLLIMPORT const uint8 pg_number_of_ones[256];
 
+#if defined(HAVE__BUILTIN_CLZ) || defined(_MSC_VER)
+#define FAST_BITSCAN_REVERSE
+#endif
+
 /*
  * pg_leftmost_one_pos32
  *		Returns the position of the most significant set bit in "word",
@@ -36,7 +40,7 @@ pg_leftmost_one_pos32(uint32 word)
 	unsigned char non_zero; // XXX can this be bool?
 #endif
 
-#if !defined(HAVE__BUILTIN_CLZ) || defined(USE_ASSERT_CHECKING)
+#if !defined(FAST_BITSCAN_REVERSE) || defined(USE_ASSERT_CHECKING)
 	int			result;
 	int			shift = 32 - 8;
 
@@ -48,18 +52,18 @@ pg_leftmost_one_pos32(uint32 word)
 	result = shift + pg_leftmost_one_pos[(word >> shift) & 255];
 #endif
 
-#if defined(HAVE__BUILTIN_CLZ)
-	bitscan_result = 31 - __builtin_clz(word);
-	Assert(bitscan_result == result);
-	return bitscan_result;
-#elif defined(_MSC_VER)
+#ifdef FAST_BITSCAN_REVERSE
+#if defined(_MSC_VER)
 	non_zero = _BitScanReverse(&bitscan_result, word);
 	Assert(non_zero);
+#elif defined(HAVE__BUILTIN_CLZ)
+	bitscan_result = 31 - __builtin_clz(word);
+#endif
 	Assert(bitscan_result == result);
 	return bitscan_result;
 #else
 	return result;
-#endif							/* HAVE__BUILTIN_CLZ */
+#endif							/* FAST_BITSCAN_REVERSE */
 }
 
 /*
@@ -76,7 +80,7 @@ pg_leftmost_one_pos64(uint64 word)
 	unsigned char non_zero; // XXX can this be bool?
 #endif
 
-#if !defined(HAVE__BUILTIN_CLZ) || defined(USE_ASSERT_CHECKING)
+#if !defined(FAST_BITSCAN_REVERSE) || defined(USE_ASSERT_CHECKING)
 	int			result;
 	int			shift = 64 - 8;
 
@@ -88,26 +92,30 @@ pg_leftmost_one_pos64(uint64 word)
 	result = shift + pg_leftmost_one_pos[(word >> shift) & 255];
 #endif
 
-#if defined(HAVE__BUILTIN_CLZ)
+#ifdef FAST_BITSCAN_REVERSE
+#if defined(_MSC_VER)
+	non_zero = _BitScanReverse64(&bitscan_result, word);
+	Assert(non_zero);
+#elif defined(HAVE__BUILTIN_CLZ)
 #if defined(HAVE_LONG_INT_64)
 	bitscan_result = 63 - __builtin_clzl(word);
 #elif defined(HAVE_LONG_LONG_INT_64)
 	bitscan_result = 63 - __builtin_clzll(word);
 #else
 #error must have a working 64-bit integer datatype
-#endif							/* HAVE_LONG_... */
-	Assert(bitscan_result == result);
-	return bitscan_result;
-#elif defined(_MSC_VER)
-	non_zero = _BitScanReverse64(&bitscan_result, word);
-	Assert(non_zero);
+#endif							/* HAVE_LONG_INT_64 */
+#endif							/* _MSC_VER */
 	Assert(bitscan_result == result);
 	return bitscan_result;
 #else
 	return result;
-#endif							/* HAVE__BUILTIN_CLZ */
+#endif							/* FAST_BITSCAN_REVERSE */
 }
 
+#if defined(HAVE__BUILTIN_CTZ) || defined(_MSC_VER)
+#define FAST_BITSCAN_FORWARD
+#endif
+
 /*
  * pg_rightmost_one_pos32
  *		Returns the position of the least significant set bit in "word",
@@ -125,7 +133,7 @@ pg_rightmost_one_pos32(uint32 word)
 	unsigned char non_zero; // XXX can this be bool?
 #endif
 
-#if !defined(HAVE__BUILTIN_CTZ) || defined(USE_ASSERT_CHECKING)
+#if !defined(FAST_BITSCAN_FORWARD) || defined(USE_ASSERT_CHECKING)
 	int			result = 0;
 
 	Assert(word != 0);
@@ -138,18 +146,18 @@ pg_rightmost_one_pos32(uint32 word)
 	result += pg_rightmost_one_pos[word & 255];
 #endif
 
-#if defined(HAVE__BUILTIN_CTZ)
-	bitscan_result = __builtin_ctz(orig_word);
-	Assert(bitscan_result == result);
-	return bitscan_result;
-#elif defined(_MSC_VER)
+#ifdef FAST_BITSCAN_FORWARD
+#if defined(_MSC_VER)
 	non_zero = _BitScanForward(&bitscan_result, orig_word);
 	Assert(non_zero);
+#elif defined(HAVE__BUILTIN_CTZ)
+	bitscan_result = __builtin_ctz(orig_word);
+#endif
 	Assert(bitscan_result == result);
 	return bitscan_result;
 #else
 	return result;
-#endif							/* HAVE__BUILTIN_CTZ */
+#endif							/* FAST_BITSCAN_FORWARD */
 }
 
 /*
@@ -168,7 +176,7 @@ pg_rightmost_one_pos64(uint64 word)
 	unsigned char non_zero; // XXX can this be bool?
 #endif
 
-#if !defined(HAVE__BUILTIN_CTZ) || defined(USE_ASSERT_CHECKING)
+#if !defined(FAST_BITSCAN_FORWARD) || defined(USE_ASSERT_CHECKING)
 	int			result = 0;
 
 	Assert(word != 0);
@@ -181,24 +189,24 @@ pg_rightmost_one_pos64(uint64 word)
 	result += pg_rightmost_one_pos[word & 255];
 #endif
 
-#ifdef HAVE__BUILTIN_CTZ
+#ifdef FAST_BITSCAN_FORWARD
+#if defined(_MSC_VER)
+	non_zero = _BitScanForward64(&bitscan_result, orig_word);
+	Assert(non_zero);
+#elif HAVE__BUILTIN_CTZ
 #if defined(HAVE_LONG_INT_64)
 	bitscan_result = __builtin_ctzl(orig_word);
 #elif defined(HAVE_LONG_LONG_INT_64)
 	bitscan_result = __builtin_ctzll(orig_word);
 #else
 #error must have a working 64-bit integer datatype
-#endif							/* HAVE_LONG_... */
-	Assert(bitscan_result == result);
-	return bitscan_result;
-#elif defined(_MSC_VER)
-	non_zero = _BitScanForward64(&bitscan_result, orig_word);
-	Assert(non_zero);
+#endif							/* HAVE_LONG_INT_64 */
+#endif							/* _MSC_VER */
 	Assert(bitscan_result == result);
 	return bitscan_result;
 #else
 	return result;
-#endif							/* HAVE__BUILTIN_CTZ */
+#endif							/* FAST_BITSCAN_FORWARD */
 }
 
 /*
-- 
2.39.0