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target/ppc: Zero second doubleword in DFP instructions

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Starting at PowerISA v3.1, the second doubleword of the registers
used to store results in DFP instructions are supposed to be zeroed.

From the ISA, chapter 7.2.1.1 Floating-Point Registers:
"""
Chapter 4. Floating-Point Facility provides 32 64-bit
FPRs. Chapter 5. Decimal Floating-Point also employs
FPRs in decimal floating-point (DFP) operations. When
VSX is implemented, the 32 FPRs are mapped to
doubleword 0 of VSRs 0-31. (...)
All instructions that operate on an FPR are redefined
to operate on doubleword element 0 of the
corresponding VSR. (...)
and the contents of doubleword element 1 of the
VSR corresponding to the target FPR or FPR pair for these
instructions are set to 0.
"""

Before, the result stored at doubleword 1 was said to be undefined.

With that, this patch changes the DFP facility to zero doubleword 1
when using set_dfp64 and set_dfp128. This fixes the behavior for ISA
3.1 while keeping the behavior correct for previous ones.

Signed-off-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220906125523.38765-4-victor.colombo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
This commit is contained in:
Víctor Colombo 2022-09-06 09:55:18 -03:00 committed by Daniel Henrique Barboza
parent 228ab1451d
commit 34f760bac2
1 changed files with 4 additions and 1 deletions
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5
target/ppc/dfp_helper.c
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@ -42,13 +42,16 @@ static void get_dfp128(ppc_vsr_t *dst, ppc_fprp_t *dfp)
static void set_dfp64(ppc_fprp_t *dfp, ppc_vsr_t *src)
{
dfp->VsrD(0) = src->VsrD(1);
dfp[0].VsrD(0) = src->VsrD(1);
dfp[0].VsrD(1) = 0ULL;
}
static void set_dfp128(ppc_fprp_t *dfp, ppc_vsr_t *src)
{
dfp[0].VsrD(0) = src->VsrD(0);
dfp[1].VsrD(0) = src->VsrD(1);
dfp[0].VsrD(1) = 0ULL;
dfp[1].VsrD(1) = 0ULL;
}
static void set_dfp128_to_avr(ppc_avr_t *dst, ppc_vsr_t *src)