From: usa@... Date: 2017-06-30T11:08:40+00:00 Subject: [ruby-core:81856] [Ruby trunk Bug#13545] Ruby built by clang 4.0.0 parses Float literal wrongly Issue #13545 has been updated by usa (Usaku NAKAMURA). Backport changed from 2.2: REQUIRED, 2.3: REQUIRED, 2.4: REQUIRED to 2.2: REQUIRED, 2.3: DONE, 2.4: REQUIRED ruby_2_3 r59224 merged revision(s) 58796. ---------------------------------------- Bug #13545: Ruby built by clang 4.0.0 parses Float literal wrongly https://bugs.ruby-lang.org/issues/13545#change-65578 * Author: mame (Yusuke Endoh) * Status: Closed * Priority: Normal * Assignee: * Target version: * ruby -v: * Backport: 2.2: REQUIRED, 2.3: DONE, 2.4: REQUIRED ---------------------------------------- ~~~ $ ./configure --prefix=/home/mame/work/local CC=clang $ make -j 4 miniruby $ ./miniruby -e 'p 1.1851510441583988e+30' 1.1851510441583981e+30 ~~~ See the last digit. While the original literal ends with "8e+30", the result ends with "1e+30". The version of clang is 4.0.0-1ubuntu1. There seems to be a bug in `ruby_strtod`. It manipulates a double variable as an integer variable by using cast. I think that this is undefined behavior, and clang seems to optimize some operations out. We can fix this issue by adding `volatile` to its variable declaration, but I'm unsure if this is a good solution. ~~~ diff --git a/util.c b/util.c index 4ae7c4fc96..ecd55bb0c5 100644 --- a/util.c +++ b/util.c @@ -1832,7 +1832,7 @@ d2b(double d_, int *e, int *bits) static double ratio(Bigint *a, Bigint *b) { - double_u da, db; + volatile double_u da, db; int k, ka, kb; dval(da) = b2d(a, &ka); ~~~ -- https://bugs.ruby-lang.org/ Unsubscribe: