Bring some MSVC asserts in line with other platforms

MSVC's _BitScan* functions return a boolean indicating whether any
bits were set in the input, and we were previously asserting that
they returned true, per our API. This is correct. However, other
platforms simply assert that the input is non-zero, so do that to be
more consistent.

Noted while investigating a hypothesis from Ranier Vilela about
undefined behavior, but this is not his proposed .

Discussion: https://www.postgresql.org/message-id/CAEudQAoDhUZyKGJ1vbMGcgVUOcsixe-%3DjcVaDWarqkUg163D2w%40mail.gmail.com

diff --git a/src/include/port/pg_bitutils.h b/src/include/port/pg_bitutils.h
index 21a4fa0341059c722be99a61665edeb5f23c7a8f..4f1a13dba939fdffb0fc96b574b37a1f95bdb2b0 100644 (file)
--- a/src/include/port/pg_bitutils.h
+++ b/src/include/port/pg_bitutils.h
@@ -48,8 +48,9 @@ pg_leftmost_one_pos32(uint32 word)
    unsigned long result;
    bool        non_zero;
 
+   Assert(word != 0);
+
    non_zero = _BitScanReverse(&result, word);
-   Assert(non_zero);
    return (int) result;
 #else
    int         shift = 32 - 8;
@@ -85,8 +86,9 @@ pg_leftmost_one_pos64(uint64 word)
    unsigned long result;
    bool        non_zero;
 
+   Assert(word != 0);
+
    non_zero = _BitScanReverse64(&result, word);
-   Assert(non_zero);
    return (int) result;
 #else
    int         shift = 64 - 8;
@@ -116,8 +118,9 @@ pg_rightmost_one_pos32(uint32 word)
    unsigned long result;
    bool        non_zero;
 
+   Assert(word != 0);
+
    non_zero = _BitScanForward(&result, word);
-   Assert(non_zero);
    return (int) result;
 #else
    int         result = 0;
@@ -156,8 +159,9 @@ pg_rightmost_one_pos64(uint64 word)
    unsigned long result;
    bool        non_zero;
 
+   Assert(word != 0);
+
    non_zero = _BitScanForward64(&result, word);
-   Assert(non_zero);
    return (int) result;
 #else
    int         result = 0;