Boost C++ Libraries: Ticket #7785: karma real generator limits precision to digits10 no matter exponent

strk@… — Tue, 11 Dec 2012 10:55:19 GMT

For reference, the problem showed up here: https://github.com/mapnik/mapnik/pull/1632 where we're trying to get an output comparable with that of iostream with setprecision(16)

anonymous — Thu, 13 Dec 2012 10:50:26 GMT

On further analysis I found out that the "fraction_part" function does not even get more than 13 significant digits when the number is lower than 10e-3, so there's nothing an overridden fraction_part method could do

Thu, 13 Dec 2012 12:44:11 GMT

The problem is in call_n, where fractional part is normalized even if the format flag is requesting fixed precision, despite the comment above (saying normalization is only needed for scientific notation).

This patch would fix my case:

--- real_utils.hpp.000  2012-12-13 13:42:01.000000000 +0100
+++ real_utils.hpp      2012-12-13 13:43:02.000000000 +0100
@@ -85,5 +85,5 @@
             // get correct precision for generated number
             unsigned precision = p.precision(n);
-            if (std::numeric_limits<U>::digits10)
+            if (std::numeric_limits<U>::digits10 && !(Policies::fmtflags::fixed & flags))
             {
                 // limit generated precision to digits10, if defined

owner changed

Joel de Guzman — Thu, 13 Dec 2012 14:32:24 GMT

owner changed from Joel de Guzman to Hartmut Kaiser

status changed; resolution set

Joel de Guzman — Sun, 14 Mar 2021 19:56:04 GMT

status new → closed
resolution → fixed

fixed in #586 https://github.com/boostorg/spirit/pull/586