Bug #19878: Math.log is broken for bignum

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.3.0dev (2023-09-04T01:35:26Z master 2ac3e9abe9) [x86_64-linux]
• Backport: 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONTNEED

[mame (Yusuke Endoh)]

p Math.log(2 ** 1020, 10) #=> 307.0505955772608
p Math.log(2 ** 1021, 10) #=> 307.35162557292483
p Math.log(2 ** 1022, 10) #=> 307.6526555685888
p Math.log(2 ** 1023, 10) #=> 688.6994720982339 <- WHAT!?
p Math.log(2 ** 1024, 10) #=> 689.3926192787939
p Math.log(2 ** 1025, 10) #=> 690.0857664593537

[mame (Yusuke Endoh)]

https://github.com/ruby/ruby/pull/8429

[mame (Yusuke Endoh)]

• Backport changed from 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN to 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONTNEED

[mame (Yusuke Endoh)]

Fortunately, this bug was introduced this year on da39936ce165ea9462b9e192eb6b608485c94842 so no need to backport.

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

Applied in changeset git|411572661a3995a0daacb6c866ea3ac6b52ad25b.

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math.c: Fix Math.log against huge bignum [Bug #19878]