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[PATCH v8.0.1 19/36] softfloat: Fix the incorrect computation in float32
From: |
Michael Tokarev |
Subject: |
[PATCH v8.0.1 19/36] softfloat: Fix the incorrect computation in float32_exp2 |
Date: |
Wed, 17 May 2023 11:00:39 +0300 |
From: Shivaprasad G Bhat <sbhat@linux.ibm.com>
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>
(cherry picked from commit 1098cc3fcf952763fc9fd72c1c8fda30a18cc8ea)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
fpu/softfloat.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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);
}
--
2.39.2
- [PATCH v8.0.1 05/36] acpi: pcihp: allow repeating hot-unplug requests, (continued)
- [PATCH v8.0.1 05/36] acpi: pcihp: allow repeating hot-unplug requests, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 11/36] hw/arm/boot: Make write_bootloader() public as arm_write_bootloader(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 16/36] hw/sd/allwinner-sdhost: Correctly byteswap descriptor fields, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 23/36] block: bdrv/blk_co_unref() for calls in coroutine context, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 14/36] hw/intc/allwinner-a10-pic: Don't use set_bit()/clear_bit(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 22/36] block: Consistently call bdrv_activate() outside coroutine, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 20/36] meson: leave unnecessary modules out of the build, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 18/36] block/export: call blk_set_dev_ops(blk, NULL, NULL), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 21/36] block: Fix use after free in blockdev_mark_auto_del(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 15/36] target/arm: Define and use new load_cpu_field_low32(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 19/36] softfloat: Fix the incorrect computation in float32_exp2,
Michael Tokarev <=
- [PATCH v8.0.1 24/36] block: Don't call no_coroutine_fns in qmp_block_resize(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 13/36] hw/arm/raspi: Use arm_write_bootloader() to write boot code, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 17/36] hw/net/allwinner-sun8i-emac: Correctly byteswap descriptor fields, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 28/36] accel/tcg: Fix atomic_mmu_lookup for reads, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 27/36] hw/pci-bridge: pci_expander_bridge fix type in pxb_cxl_dev_reset(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 26/36] target/riscv: Restore the predicate() NULL check behavior, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 29/36] target/arm: Fix handling of SW and NSW bits for stage 2 walks, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 25/36] target/riscv: Fix itrigger when icount is used, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 30/36] ui: Fix pixel colour channel order for PNG screenshots, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 31/36] target/arm: Correct AArch64.S2MinTxSZ 32-bit EL1 input size check, Michael Tokarev, 2023/05/17