| Issue |
86871
|
| Summary |
[builtins] divtc3 accuracy issue
|
| Labels |
compiler-rt:builtins
|
| Assignees |
|
| Reporter |
vzakhari
|
I am getting quite incorrect result for `_Complex __float128` division with clang 17.0.6. GCC 13.2.0 version returns closer result.
I used libquadmath for printing the results. Here is a reproducer:
```
#include <complex.h>
#include <quadmath.h>
#include <stdio.h>
#define complex128 _Complex __float128
int main() {
char buffer[1000];
complex128 z1 = {4.181214e+4931Q, -1.113838e+4932Q};
complex128 z2 = {-1.113838e+4932Q, -4.181214e+4931Q};
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __real__ z1);
printf("z1: %s ", buffer);
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __imag__ z1);
printf("%s\n", buffer);
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __real__ z2);
printf("z2: %s ", buffer);
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __imag__ z2);
printf("%s\n", buffer);
z1 /= z2;
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __real__ z1);
printf("z1/z2: %s ", buffer);
quadmath_snprintf(buffer, sizeof buffer, "%.6Qe", __imag__ z1);
printf("%s\n", buffer);
return 0;
}
```
Compilation with `clang testdiv.c -I ${GCC_INSTALL}/lib/gcc/x86_64-pc-linux-gnu/13.2.0/include ${GCC_INSTALL}/lib64/libquadmath.a -lm --gcc-toolchain=${GCC_INSTALL}`:
```
z1: 4.181214e+4931 -1.113838e+4932
z2: -1.113838e+4932 -4.181214e+4931
z1/z2: -0.000000e+00 1.000000e+00
```
This is close to the correct mathematical result: https://www.wolframalpha.com/input?i=%284.181214e%2B4931+-1.113838e%2B4932i%29%2F%28-1.113838e%2B4932+-4.181214e%2B4931i%29
When I link the builtins library with `clang testdiv.c -I ${GCC_INSTALL}/lib/gcc/x86_64-pc-linux-gnu/13.2.0/include ${GCC_INSTALL}/lib64/libquadmath.a -lm ${CLANG_INSTALL}/lib/clang/17/lib/x86_64-unknown-linux-gnu/libclang_rt.builtins.a --gcc-toolchain=${GCC_INSTALL}` I get this:
```
z1: 4.181214e+4931 -1.113838e+4932
z2: -1.113838e+4932 -4.181214e+4931
z1/z2: 1.680232e-4932 1.680232e-4932
```
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