The following code produces a warning about precision loss in an int-to-float
conversion:
$cat warn.cpp
float f(float x, unsigned short y)
{
return x * y;
}
$g++ -Wconversion -c -o warn.o warn.cpp
warn.cpp: In function float f(float, short unsigned int):
warn.cpp:3: warning: conversion to float from int may alter its value
$
The code snippet does not have an int-to-float conversion.
It does have an unsigned short-to-float conversion according to the C++
standard, chapter 5 [expr] para 9: "[inapplicable note on long double and
double...] Otherwise, if either operand is float, the other shall be converted
to float [...]". Only after this rule, integral promotions are performed, which
could promote the unsigned short to an int.
Moreover, he conversion does not lose information since the 16 bits of the
unsigned short fit amply in the float's mantissa.
Not tested with other shorter-than-int types. This problem might apply there as
well...
--
Summary: Spurious integral promotion
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: zweije at xs4all dot nl
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41779
