| Message ID | 20200523201712.23908-1-vr_qemu@t-online.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | audio/mixeng: fix clang 10+ warning | expand |
On Sat, May 23, 2020 at 10:17:12PM +0200, Volker Rümelin wrote: > The code in CONV_NATURAL_FLOAT() and CLIP_NATURAL_FLOAT() > seems to use the constant 2^31-0.5 to convert float to integer > and back. But the float type lacks the required precision and > the constant used for the conversion is 2^31. This is equiva- > lent to a [-1.f, 1.f] <-> [INT32_MIN, INT32_MAX + 1] mapping. > > This patch explicitly writes down the used constant. The > compiler generated code doesn't change. > > The constant 2^31 has an exact float representation and the > clang 10 compiler stops complaining about an implicit int to > float conversion with a changed value. > > A few notes: > - The conversion of 1.f to INT32_MAX + 1 doesn't overflow. The > type of the destination variable is int64_t. > - At a later stage one of the clip_* functions in > audio/mixeng_template.h limits INT32_MAX + 1 to the integer > range. > - The clip_natural_float_* functions in audio/mixeng.c convert > INT32_MAX and INT32_MAX + 1 to 1.f. > > Buglink: https://bugs.launchpad.net/bugs/1878627 > Signed-off-by: Volker Rümelin <vr_qemu@t-online.de> Added to audio queue. thanks, Gerd
diff --git a/audio/mixeng.c b/audio/mixeng.c index 739a500449..924dcb858a 100644 --- a/audio/mixeng.c +++ b/audio/mixeng.c @@ -271,11 +271,12 @@ f_sample *mixeng_clip[2][2][2][3] = { #define CONV_NATURAL_FLOAT(x) (x) #define CLIP_NATURAL_FLOAT(x) (x) #else -static const float float_scale = UINT_MAX / 2.f; +/* macros to map [-1.f, 1.f] <-> [INT32_MIN, INT32_MAX + 1] */ +static const float float_scale = (int64_t)INT32_MAX + 1; #define CONV_NATURAL_FLOAT(x) ((x) * float_scale) #ifdef RECIPROCAL -static const float float_scale_reciprocal = 2.f / UINT_MAX; +static const float float_scale_reciprocal = 1.f / ((int64_t)INT32_MAX + 1); #define CLIP_NATURAL_FLOAT(x) ((x) * float_scale_reciprocal) #else #define CLIP_NATURAL_FLOAT(x) ((x) / float_scale)
The code in CONV_NATURAL_FLOAT() and CLIP_NATURAL_FLOAT() seems to use the constant 2^31-0.5 to convert float to integer and back. But the float type lacks the required precision and the constant used for the conversion is 2^31. This is equiva- lent to a [-1.f, 1.f] <-> [INT32_MIN, INT32_MAX + 1] mapping. This patch explicitly writes down the used constant. The compiler generated code doesn't change. The constant 2^31 has an exact float representation and the clang 10 compiler stops complaining about an implicit int to float conversion with a changed value. A few notes: - The conversion of 1.f to INT32_MAX + 1 doesn't overflow. The type of the destination variable is int64_t. - At a later stage one of the clip_* functions in audio/mixeng_template.h limits INT32_MAX + 1 to the integer range. - The clip_natural_float_* functions in audio/mixeng.c convert INT32_MAX and INT32_MAX + 1 to 1.f. Buglink: https://bugs.launchpad.net/bugs/1878627 Signed-off-by: Volker Rümelin <vr_qemu@t-online.de> --- audio/mixeng.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)