[FFmpeg-devel] [PATCH] avfilter/showcqt: BASEFREQ and ENDFREQ cast to double

Michael Niedermayer michaelni at gmx.at
Mon Nov 30 18:51:36 CET 2015

On Mon, Nov 30, 2015 at 06:25:15PM +0100, Michael Niedermayer wrote:
> On Mon, Nov 30, 2015 at 04:52:20PM +0100, Nicolas George wrote:
> > Le decadi 10 frimaire, an CCXXIV, Muhammad Faiz a écrit :
> > > -    if (s->basefreq != BASEFREQ || s->endfreq != ENDFREQ) {
> > > +    if (s->basefreq != (double) BASEFREQ || s->endfreq != (double) ENDFREQ) {
> > 
> > Looks wrong to me. Since s->basefreq is double and operands are always
> > converted to the largest type before comparison, the cast would be implicit.
> > And BASEFREQ and ENDFREQ are double anyway.
> > 
> > The problem, if any, is somewhere else.
> ISO/IEC 9899:TC3
> Characteristics of floating types <float.h>
>     8 Except for assignment and cast (which remove all extra range and precision), the values
>     of operations with floating operands and values subject to the usual arithmetic
>     conversions and of floating constants are evaluated to a format whose range and precision
>     may be greater than required by the type. The use of evaluation formats is characterized
>     by the implementation-defined value of FLT_EVAL_METHOD:19)
>         -1       indeterminable;
>         0       evaluate all operations and constants just to the range and precision of the
>                 type;
>         1       evaluate operations and constants of type float and double to the
>                 range and precision of the double type, evaluate long double
>                 operations and constants to the range and precision of the long double
>                 type;
>         2       evaluate all operations and constants to the range and precision of the
>                 long double type.
>     All other negative values for FLT_EVAL_METHOD characterize implementation-defined
>     behavior.

a few more related parts:
    5 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
    <math.h> and <complex.h> that return floating-point results is implementation-
    defined, as is the accuracy of the conversion between floating-point internal
    representations and string representations performed by the library functions in
    <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
    accuracy is unknown. Floating constants
    7 The translation-time conversion of floating constants should match the execution-time
    conversion of character strings by library functions, such as strtod, given matching
    inputs suitable for both conversions, the same result format, and default execution-time

> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> Republics decline into democracies and democracies degenerate into
> despotisms. -- Aristotle

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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