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>
---
target/ppc/dfp_helper.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/target/ppc/dfp_helper.c b/target/ppc/dfp_helper.c
index 5ba74b2124..be7aa5357a 100644
--- a/target/ppc/dfp_helper.c
+++ b/target/ppc/dfp_helper.c
@@ -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)