diff options
| author | Shivaprasad G Bhat <sbhat@linux.ibm.com> | 2023-05-02 20:55:30 +0530 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2023-05-05 16:57:48 +0100 |
| commit | 1098cc3fcf952763fc9fd72c1c8fda30a18cc8ea (patch) | |
| tree | ee321efbc0b57203b7be14bb39850319f05c94fc /fpu | |
| parent | a9fe9e191b4305b88c356a1ed9ac3baf89eb18aa (diff) | |
softfloat: Fix the incorrect computation in float32_exp2
The float32_exp2 function is computing wrong exponent of 2.
For example, with the following set of values {0.1, 2.0, 2.0, -1.0},
the expected output would be {1.071773, 4.000000, 4.000000, 0.500000}.
Instead, the function is computing {1.119102, 3.382044, 3.382044, -0.191022}
Looking at the code, the float32_exp2() attempts to do this
2 3 4 5 n
x x x x x x x
e = 1 + --- + --- + --- + --- + --- + ... + --- + ...
1! 2! 3! 4! 5! n!
But because of the typo it ends up doing
x x x x x x x
e = 1 + --- + --- + --- + --- + --- + ... + --- + ...
1! 2! 3! 4! 5! n!
This is because instead of the xnp which holds the numerator, parts_muladd
is using the xp which is just 'x'. Commit '572c4d862ff2' refactored this
function, and mistakenly used xp instead of xnp.
Cc: qemu-stable@nongnu.org
Fixes: 572c4d862ff2 "softfloat: Convert float32_exp2 to FloatParts"
Partially-Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1623
Reported-By: Luca Barbato (https://gitlab.com/lu-zero)
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Message-Id: <168304110865.537992.13059030916325018670.stgit@localhost.localdomain>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Diffstat (limited to 'fpu')
| -rw-r--r-- | fpu/softfloat.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c index c7454c3eb1..108f9cb224 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -5135,7 +5135,7 @@ float32 float32_exp2(float32 a, float_status *status) float64_unpack_canonical(&rp, float64_one, status); for (i = 0 ; i < 15 ; i++) { float64_unpack_canonical(&tp, float32_exp2_coefficients[i], status); - rp = *parts_muladd(&tp, &xp, &rp, 0, status); + rp = *parts_muladd(&tp, &xnp, &rp, 0, status); xnp = *parts_mul(&xnp, &xp, status); } |