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[committed] libstdc++: Do not call log10(0.0) in std::format [PR110860]

Message ID 20230811172221.1432932-1-jwakely@redhat.com
State Unresolved
Headers
Series [committed] libstdc++: Do not call log10(0.0) in std::format [PR110860] |

Checks

Context Check Description
snail/gcc-patch-check warning Git am fail log

Commit Message

Jonathan Wakely Aug. 11, 2023, 5:21 p.m. UTC 
  Second attempt to fix this PR. Tested x86_64-linux, pushed to trunk.

-- >8 --

Calling log10(0.0) returns -inf which has undefined behaviour when
converted to an integer. We only need to use log10 for large values
anyway. If the value is zero then the larger buffer is only needed due
to a large precision, so we don't need to use log10 to estimate the
number of digits for the significand.

libstdc++-v3/ChangeLog:

	PR libstdc++/110860
	* include/std/format (__formatter_fp::format): Do not call log10
	with zero values.
---
 libstdc++-v3/include/std/format | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 2fe430f75f6..23da6b008c5 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -1490,7 +1490,7 @@  namespace __format
 	      // If the buffer is too small it's probably because of a large
 	      // precision, or a very large value in fixed format.
 	      size_t __guess = 8 + __prec;
-	      if (__fmt == chars_format::fixed) // +ddd.prec
+	      if (__fmt == chars_format::fixed && __v != 0) // +ddd.prec
 		{
 		  if constexpr (is_same_v<_Fp, float>)
 		    __guess += __builtin_log10f(__v < 0.0f ? -__v : __v);