[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PULL 14/39] target/i386: DPPS rounding fix
From: |
Paolo Bonzini |
Subject: |
[PULL 14/39] target/i386: DPPS rounding fix |
Date: |
Thu, 1 Sep 2022 20:24:04 +0200 |
The DPPS (Dot Product) instruction is defined to first sum pairs of
intermediate results, then sum those values to get the final result.
i.e. (A+B)+(C+D)
We incrementally sum the results, i.e. ((A+B)+C)+D, which can result
in incorrect rouding.
For consistency, also change the variable names to the ones used
in the Intel SDM and implement DPPD following the manual.
Based on a patch by Paul Brook <paul@nowt.org>.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
target/i386/ops_sse.h | 67 ++++++++++++++++++++++---------------------
1 file changed, 35 insertions(+), 32 deletions(-)
diff --git a/target/i386/ops_sse.h b/target/i386/ops_sse.h
index 2524db4c25..b12b271fcd 100644
--- a/target/i386/ops_sse.h
+++ b/target/i386/ops_sse.h
@@ -1943,56 +1943,59 @@ SSE_HELPER_I(helper_pblendw, W, 8, FBLENDP)
void glue(helper_dpps, SUFFIX)(CPUX86State *env, Reg *d, Reg *s, uint32_t mask)
{
- float32 iresult = float32_zero;
+ float32 prod1, prod2, temp2, temp3, temp4;
+ /*
+ * We must evaluate (A+B)+(C+D), not ((A+B)+C)+D
+ * to correctly round the intermediate results
+ */
if (mask & (1 << 4)) {
- iresult = float32_add(iresult,
- float32_mul(d->ZMM_S(0), s->ZMM_S(0),
- &env->sse_status),
- &env->sse_status);
+ prod1 = float32_mul(d->ZMM_S(0), s->ZMM_S(0), &env->sse_status);
+ } else {
+ prod1 = float32_zero;
}
if (mask & (1 << 5)) {
- iresult = float32_add(iresult,
- float32_mul(d->ZMM_S(1), s->ZMM_S(1),
- &env->sse_status),
- &env->sse_status);
+ prod2 = float32_mul(d->ZMM_S(1), s->ZMM_S(1), &env->sse_status);
+ } else {
+ prod2 = float32_zero;
}
+ temp2 = float32_add(prod1, prod2, &env->sse_status);
if (mask & (1 << 6)) {
- iresult = float32_add(iresult,
- float32_mul(d->ZMM_S(2), s->ZMM_S(2),
- &env->sse_status),
- &env->sse_status);
+ prod1 = float32_mul(d->ZMM_S(2), s->ZMM_S(2), &env->sse_status);
+ } else {
+ prod1 = float32_zero;
}
if (mask & (1 << 7)) {
- iresult = float32_add(iresult,
- float32_mul(d->ZMM_S(3), s->ZMM_S(3),
- &env->sse_status),
- &env->sse_status);
+ prod2 = float32_mul(d->ZMM_S(3), s->ZMM_S(3), &env->sse_status);
+ } else {
+ prod2 = float32_zero;
}
- d->ZMM_S(0) = (mask & (1 << 0)) ? iresult : float32_zero;
- d->ZMM_S(1) = (mask & (1 << 1)) ? iresult : float32_zero;
- d->ZMM_S(2) = (mask & (1 << 2)) ? iresult : float32_zero;
- d->ZMM_S(3) = (mask & (1 << 3)) ? iresult : float32_zero;
+ temp3 = float32_add(prod1, prod2, &env->sse_status);
+ temp4 = float32_add(temp2, temp3, &env->sse_status);
+
+ d->ZMM_S(0) = (mask & (1 << 0)) ? temp4 : float32_zero;
+ d->ZMM_S(1) = (mask & (1 << 1)) ? temp4 : float32_zero;
+ d->ZMM_S(2) = (mask & (1 << 2)) ? temp4 : float32_zero;
+ d->ZMM_S(3) = (mask & (1 << 3)) ? temp4 : float32_zero;
}
void glue(helper_dppd, SUFFIX)(CPUX86State *env, Reg *d, Reg *s, uint32_t mask)
{
- float64 iresult = float64_zero;
+ float64 prod1, prod2, temp2;
if (mask & (1 << 4)) {
- iresult = float64_add(iresult,
- float64_mul(d->ZMM_D(0), s->ZMM_D(0),
- &env->sse_status),
- &env->sse_status);
+ prod1 = float64_mul(d->ZMM_D(0), s->ZMM_D(0), &env->sse_status);
+ } else {
+ prod1 = float64_zero;
}
if (mask & (1 << 5)) {
- iresult = float64_add(iresult,
- float64_mul(d->ZMM_D(1), s->ZMM_D(1),
- &env->sse_status),
- &env->sse_status);
+ prod2 = float64_mul(d->ZMM_D(1), s->ZMM_D(1), &env->sse_status);
+ } else {
+ prod2 = float64_zero;
}
- d->ZMM_D(0) = (mask & (1 << 0)) ? iresult : float64_zero;
- d->ZMM_D(1) = (mask & (1 << 1)) ? iresult : float64_zero;
+ temp2 = float64_add(prod1, prod2, &env->sse_status);
+ d->ZMM_D(0) = (mask & (1 << 0)) ? temp2 : float64_zero;
+ d->ZMM_D(1) = (mask & (1 << 1)) ? temp2 : float64_zero;
}
void glue(helper_mpsadbw, SUFFIX)(CPUX86State *env, Reg *d, Reg *s,
--
2.37.2
- [PULL 03/39] scsi: Reject commands if the CDB length exceeds buf_len, (continued)
- [PULL 03/39] scsi: Reject commands if the CDB length exceeds buf_len, Paolo Bonzini, 2022/09/01
- [PULL 04/39] i386: reset KVM nested state upon CPU reset, Paolo Bonzini, 2022/09/01
- [PULL 02/39] scsi: Add buf_len parameter to scsi_req_new(), Paolo Bonzini, 2022/09/01
- [PULL 06/39] configure: improve error for ucontext coroutine backend, Paolo Bonzini, 2022/09/01
- [PULL 05/39] i386: do kvm_put_msr_feature_control() first thing when vCPU is reset, Paolo Bonzini, 2022/09/01
- [PULL 07/39] meson: be strict for boolean options, Paolo Bonzini, 2022/09/01
- [PULL 08/39] meson: remove dead code, Paolo Bonzini, 2022/09/01
- [PULL 11/39] tests/tcg: x86_64: improve consistency with i386, Paolo Bonzini, 2022/09/01
- [PULL 10/39] KVM: dirty ring: add missing memory barrier, Paolo Bonzini, 2022/09/01
- [PULL 09/39] meson: remove dead assignments, Paolo Bonzini, 2022/09/01
- [PULL 14/39] target/i386: DPPS rounding fix,
Paolo Bonzini <=
- [PULL 12/39] tests/tcg: i386: extend BMI test, Paolo Bonzini, 2022/09/01
- [PULL 13/39] target/i386: fix PHSUB* instructions with dest=src, Paolo Bonzini, 2022/09/01
- [PULL 17/39] target/i386: formatting fixes, Paolo Bonzini, 2022/09/01
- [PULL 16/39] target/i386: do not use MOVL to move data between SSE registers, Paolo Bonzini, 2022/09/01
- [PULL 15/39] tests/tcg: i386: add SSE tests, Paolo Bonzini, 2022/09/01
- [PULL 19/39] target/i386: Rework sse_op_table1, Paolo Bonzini, 2022/09/01
- [PULL 21/39] target/i386: Move 3DNOW decoder, Paolo Bonzini, 2022/09/01
- [PULL 20/39] target/i386: Rework sse_op_table6/7, Paolo Bonzini, 2022/09/01
- [PULL 22/39] target/i386: check SSE table flags instead of hardcoding opcodes, Paolo Bonzini, 2022/09/01
- [PULL 18/39] target/i386: Add ZMM_OFFSET macro, Paolo Bonzini, 2022/09/01