Re: [Tinycc-devel] Major bug in the pow function resulting in: 0.993013 = 0.860892
Vincent Lefevre wrote in
<20240105235600.gd4...@qaa.vinc17.org>:
|On 2024-01-05 13:47:25 +0100, Aurélie Tisson (BastaPrint) wrote:
|> The same calculation gives me 2 different values : 0.993013 0.860892
|> wheras it should give 0.993013 only (tells GCC).
|
|Well, your code is not portable.
You are the mathematician.
But *i* thought it was a request to release 0.9.28, given that tcc
of 20231230 gets the stuff correct?
|> #include
|> #include
|> int main(){
|> double s = .7;
|> double a = (1. - .1 * s) / (1. + .1 * s);
| ^^^ ^^^
|> double b = pow(a, .05);
|> double c = pow( ((1. - .1 * s) / (1. + .1 * s)), .05);
|^^^ ^^^
|
|> printf("%f %f \n", b, c);
|>}
|
|You should not depend on contraction of FP expressions.
|Here, GCC may generate a FMA, which generally increases
|the accuracy of the results.
I am overly happy there is no floating-point in my code.
Never in the past, not today. (Anything which was there was
thrown away.) Yay.
--steffen
|
|Der Kragenbaer,The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
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Re: [Tinycc-devel] Major bug in the pow function resulting in: 0.993013 = 0.860892
Hi,
On 2024-01-05 13:47:25 +0100, Aurélie Tisson (BastaPrint) wrote:
> The same calculation gives me 2 different values : 0.993013 0.860892
> wheras it should give 0.993013 only (tells GCC).
Well, your code is not portable.
> #include
> #include
> int main(){
> double s = .7;
> double a = (1. - .1 * s) / (1. + .1 * s);
^^^ ^^^
> double b = pow(a, .05);
> double c = pow( ((1. - .1 * s) / (1. + .1 * s)), .05);
^^^ ^^^
> printf("%f %f \n", b, c);
> }
You should not depend on contraction of FP expressions.
Here, GCC may generate a FMA, which generally increases
the accuracy of the results.
--
Vincent Lefèvre - Web:
Re: [Tinycc-devel] Major bug in the pow function resulting in: 0.993013 = 0.860892
Hello: > ==> can anyone reproduce this?I tried your code with Visual Studio (2019), > CLang (17.0.6), MinGW-w64 (GCC 13.1.0) and,of course TCC. All compilers > produce the expected result: P:\>tcc -o pow.exe pow.c P:\>pow 0.993013 0.993013 P:\>tcc -v tcc version 0.9.28rc 2023-12-09_main@8332f68* (i386 Windows) Could you try 0.9.28rc to see if its "gone" on your end too? Fred ___ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
