[Sdcc-user] Bug report on SDCC math function (expf)

Tognolini Maurizio Wed, 29 Nov 2006 20:39:26 -0800

Hello,


My name is Maurizio Tognolini and  I work in the  Geneva Engineering 
School (Switzerland). In my group we testing now the SDCC free c
compiler on our  micro controller based control system, and we encounter
some difficulties. We use as debugger en code loader the IDE free
development environment from Silicon Laboratories.

We observe an abnormal behavior using *expf *function  with SDCC
compiler (last release).
We compile the c source code for the 8051F120 micro controller from
Cygnal, with the following compilation directives:

The c compiler options:
-c --debug --use-stdout -V --model-large

The linker options:
--debug --use-stdout -V --model-large --no-xinit-opt

the assembler options:
-plosgff --model-large --xdata-loc

*The problem: *
if the argument of the expf() function is negative the result sign is
wrong (negative) for the arguments values between -0.1/3 and -2.0/3.
bellow you can find the source code of the function who use the expf in
order to compute a table of decreasing exp.
A dump of memory is attached (dumpSignalRef.txt) containing the numbers
in SignalRef[] table), the first value is OK  but the following are
wrong (negative).

We can solve this problem using positive argument in the expression
1/expf() but we need to understand  why this happens.

Last question: Do you know a debugger based on SDCC compiler for MCS51
family ?

Thanks for your help.

Sincerely

M.Tognolini
Ecole d'Ingénieurs de Genève
1202 Genève
Suisse

Tel 0041 22 3380565



#define  NBR_POINTS     100        // Nombre de points du signal de
reference
#define  AMPLITUDE     (float)512.0   // Amplitude du signal de
reference    

void SignalSinusAmorti(void)

{
    static float arg;
    char  I;

    arg = 0.0;

    for (I = 0; I < NBR_POINTS; I++)
    {
        SignalRef[I] = (int)(AMPLITUDE *expf(arg)); 
//*sinf(OMEGA*t+5*PI) + 0.5 );
        arg = arg - 0.033333;
    }
}

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[Sdcc-user] Bug report on SDCC math function (expf)

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