In perl.git, the branch blead has been updated <http://perl5.git.perl.org/perl.git/commitdiff/b27804d8b48d647c08dc853b49e5b311fe166616?hp=ba0f5503397ddc65667224047f121adc8b44784c>
- Log ----------------------------------------------------------------- commit b27804d8b48d647c08dc853b49e5b311fe166616 Author: David Mitchell <[email protected]> Date: Mon Dec 2 15:04:49 2013 +0000 [perl #120426] atof() small value rounding errors For something like 0.153e-305, which is small, but not quite the smallest number (which is around 2.2e-308), adding extra digits to the fractional part could cause unnecessary rounding to zero. From the bug report: $ echo 0.1530e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";' v=0 $ echo 0.153e-305 | perl -e '$v = <STDIN>; print "v=", $v + 0, "\n";' v=1.53e-306 This was because 0.1234e-305 is calculated as 1234 / (10^309) and 10^309 becomes infinity. In these edge cases, repeatedly decrement the exponent and divide the mantissa by 10 until the exponent becomes in range; in this case we instead calculate 123 / (10^308) ----------------------------------------------------------------------- Summary of changes: numeric.c | 11 +++++++++++ t/opbasic/arith.t | 14 +++++++++++++- 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/numeric.c b/numeric.c index c1bd581..756a86a 100644 --- a/numeric.c +++ b/numeric.c @@ -823,6 +823,17 @@ S_mulexp10(NV value, I32 exponent) if (exponent < 0) { negative = 1; exponent = -exponent; +#ifdef NV_MAX_10_EXP + /* for something like 1234 x 10^-309, the action of calculating + * the intermediate value 10^309 then returning 1234 / (10^309) + * will fail, since 10^309 becomes infinity. In this case try to + * refactor it as 123 / (10^308) etc. + */ + while (value && exponent > NV_MAX_10_EXP) { + exponent--; + value /= 10; + } +#endif } for (bit = 1; exponent; bit <<= 1) { if (exponent & bit) { diff --git a/t/opbasic/arith.t b/t/opbasic/arith.t index d85a9ba..a90e84c 100644 --- a/t/opbasic/arith.t +++ b/t/opbasic/arith.t @@ -9,7 +9,7 @@ BEGIN { # functions imported from t/test.pl or Test::More, as those programs/libraries # use operators which are what is being tested in this file. -print "1..167\n"; +print "1..175\n"; sub try ($$$) { print +($_[1] ? "ok" : "not ok"), " $_[0] - $_[2]\n"; @@ -456,3 +456,15 @@ else { print "ok ", $T++, " - infinity\n"; } + +# [perl #120426] +# small numbers shouldn't round to zero if they have extra floating digits + +try $T++, 0.153e-305 != 0.0, '0.153e-305'; +try $T++, 0.1530e-305 != 0.0, '0.1530e-305'; +try $T++, 0.15300e-305 != 0.0, '0.15300e-305'; +try $T++, 0.153000e-305 != 0.0, '0.153000e-305'; +try $T++, 0.1530000e-305 != 0.0, '0.1530000e-305'; +try $T++, 0.1530001e-305 != 0.0, '0.1530001e-305'; +try $T++, 1.17549435100e-38 != 0.0, 'min single'; +try $T++, 2.2250738585072014e-308 != 0.0, 'min double'; -- Perl5 Master Repository
