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audio/mixeng: fix clang 10+ warning
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> Message-id: 20200523201712.23908-1-vr_qemu@t-online.de Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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@ -271,11 +271,12 @@ f_sample *mixeng_clip[2][2][2][3] = {
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#define CONV_NATURAL_FLOAT(x) (x)
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#define CLIP_NATURAL_FLOAT(x) (x)
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#else
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static const float float_scale = UINT_MAX / 2.f;
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/* macros to map [-1.f, 1.f] <-> [INT32_MIN, INT32_MAX + 1] */
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static const float float_scale = (int64_t)INT32_MAX + 1;
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#define CONV_NATURAL_FLOAT(x) ((x) * float_scale)
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#ifdef RECIPROCAL
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static const float float_scale_reciprocal = 2.f / UINT_MAX;
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static const float float_scale_reciprocal = 1.f / ((int64_t)INT32_MAX + 1);
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#define CLIP_NATURAL_FLOAT(x) ((x) * float_scale_reciprocal)
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#else
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#define CLIP_NATURAL_FLOAT(x) ((x) / float_scale)
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