[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:

Ok, fbound() is now better in all branches. I also fixed all compiler warnings 
in 2.7. I close the issue.

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:


New changeset e5b79c546370521764457ea2ec809303e580f5ea by Victor Stinner in 
branch '2.7':
bpo-19418: audioop.c: Fix warnings on -0x8000 (GH-7453)
https://github.com/python/cpython/commit/e5b79c546370521764457ea2ec809303e580f5ea


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 2bc1946fb02e140f5f5ac21a1afa2763615ad16b by Victor Stinner (Miss 
Islington (bot)) in branch '3.6':
bpo-33781: audioop: enhance rounding double as int (GH-7447) (GH-7451)
https://github.com/python/cpython/commit/2bc1946fb02e140f5f5ac21a1afa2763615ad16b


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

Change by STINNER Victor :


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:

> New changeset b17d409bc0458e3981987c2358da661f228f5891 by Victor Stinner in 
> branch '2.7':
> bpo-33781: audioop: enhance rounding double as int (GH-7447) (GH-7452)

I checked AppVeyor logs: this change fixed the audioop.c warning that I wanted 
to fix ;-)

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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:


New changeset b17d409bc0458e3981987c2358da661f228f5891 by Victor Stinner in 
branch '2.7':
bpo-33781: audioop: enhance rounding double as int (GH-7447) (GH-7452)
https://github.com/python/cpython/commit/b17d409bc0458e3981987c2358da661f228f5891


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:

Note: I chose to not add a NEWS entry, because even if my change might enhance 
the rounding, I don't think that it has any effect in practice :-)

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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

Change by STINNER Victor :


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[issue33781] audioop.c: fbound() casts double to int for its return value

[miss-islington]

miss-islington  added the comment:


New changeset 5c022f13ab6db8929e092ad035b3dc61701e3198 by Miss Islington (bot) 
in branch '3.7':
bpo-33781: audioop: enhance rounding double as int (GH-7447)
https://github.com/python/cpython/commit/5c022f13ab6db8929e092ad035b3dc61701e3198


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:

> But since it is always used with floor(), it is better to move floor() inside 
> it.

Yeah, that's what I did ;-) I will backport the change to 3.7, 3.6 and 2.7. My 
final goal is just to fix a compiler warning in 2.7 :-D

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[issue33781] audioop.c: fbound() casts double to int for its return value

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

It was my mistake. fbound() should be return double.

But since it is always used with floor(), it is better to move floor() inside 
it.

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[issue33781] audioop.c: fbound() casts double to int for its return value

[miss-islington]

Change by miss-islington :


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 45e4efba7fa2abe61d25e4f8b5bf482e19ff1280 by Victor Stinner in 
branch 'master':
bpo-33781: audioop: enhance rounding double as int (GH-7447)
https://github.com/python/cpython/commit/45e4efba7fa2abe61d25e4f8b5bf482e19ff1280


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

STINNER Victor  added the comment:

Oh, fbound() cast to (int) has been done by... myself :-D

commit f2b9a340ef143099726fb642951410e4ad793c7f
Author: Victor Stinner 
Date:   Tue May 7 23:49:15 2013 +0200

audioop: explicit cast to fix a compiler warning

diff --git a/Modules/audioop.c b/Modules/audioop.c
index 7e40bbddc6..4f2b25f33a 100644
--- a/Modules/audioop.c
+++ b/Modules/audioop.c
@@ -37,7 +37,7 @@ fbound(double val, double minval, double maxval)
 val = maxval;
 else if (val < minval + 1)
 val = minval;
-return val;
+return (int)val;
 }


Stupid me!

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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

Change by STINNER Victor :


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[issue33781] audioop.c: fbound() casts double to int for its return value

[STINNER Victor]

New submission from STINNER Victor :

Extract of Python 2.7, Modules/audioop.c:

static int
fbound(double val, double minval, double maxval)
{
if (val > maxval)
val = maxval;
else if (val < minval + 1)
val = minval;
return val;
}

Example of usage:

double factor, fval, maxval, minval;
int len, size, val = 0;

fval = (double)val*factor;
val = (int)floor(fbound(fval, minval, maxval));

It seems wrong to me to call floor() with an integer. Why fbound() doesn't 
return a double?

fbound() has been modified to explicitly cast its result to an int in the 
master branch:

static int
fbound(double val, double minval, double maxval)
{
if (val > maxval)
val = maxval;
else if (val < minval + 1)
val = minval;
return (int)val;
}

But master still uses something like:

val = floor(fbound(val, minval, maxval));


It seems like fbound() result is always passed into floor(). Maybe floor() 
should be moved into fbound()?

Attached PR changes fbound() to round correctly: call floor() into fbound().

--

I looked at the code because of the following compiler warning on Python 2.7:

[00:02:21] ..\Modules\audioop.c(38): warning C4244: 'return' : conversion from 
'double' to 'int', possible loss of data 
[C:\projects\cpython\PCbuild\pythoncore.vcxproj]

--
components: Extension Modules
messages: 318808
nosy: vstinner
priority: normal
severity: normal
status: open
title: audioop.c: fbound() casts double to int for its return value
versions: Python 2.7, Python 3.6, Python 3.7, Python 3.8

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