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[Qemu-devel] [PATCH] ppc: Fix xscvdpspn for SNAN
From: |
Paul A. Clarke |
Subject: |
[Qemu-devel] [PATCH] ppc: Fix xscvdpspn for SNAN |
Date: |
Tue, 20 Aug 2019 12:26:04 -0500 |
From: "Paul A. Clarke" <address@hidden>
helper_xscvdpspn() uses float64_to_float32() to convert double-precision
floating-point to single-precision. Unfortunately, float64_to_float32()
converts SNAN to QNAN, which should not happen with xscvdpspn.
float64_to_float32() is also used by other instruction implementations
for conversions which _should_ convert SNAN to QNAN.
Rather than trying to wedge code to preserve SNAN in float64_to_float32()
just for this this one case, I instead embed an embodiment of the
conversion code outlined in the POWER ISA for xscvdpspn.
Signed-off-by: Paul A. Clarke <address@hidden>
---
target/ppc/fpu_helper.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c
index 07bc905..c8e7192 100644
--- a/target/ppc/fpu_helper.c
+++ b/target/ppc/fpu_helper.c
@@ -2887,12 +2887,40 @@ void helper_xscvqpdp(CPUPPCState *env, uint32_t opcode,
uint64_t helper_xscvdpspn(CPUPPCState *env, uint64_t xb)
{
- uint64_t result;
+ uint64_t result, sign, exp, frac;
float_status tstat = env->fp_status;
set_float_exception_flags(0, &tstat);
- result = (uint64_t)float64_to_float32(xb, &tstat);
+ sign = extract64(xb, 63, 1);
+ exp = extract64(xb, 52, 11);
+ frac = extract64(xb, 0, 52) | 0x10000000000000ULL;
+
+ if (unlikely(exp == 0 && extract64(frac, 0, 52) != 0)) {
+ /* DP denormal operand. */
+ /* Exponent override to DP min exp. */
+ exp = 1;
+ /* Implicit bit override to 0. */
+ frac = deposit64(frac, 53, 1, 0);
+ }
+
+ if (unlikely(exp < 897 && frac != 0)) {
+ /* SP tiny operand. */
+ if (897 - exp > 63) {
+ frac = 0;
+ } else {
+ /* Denormalize until exp = SP min exp. */
+ frac >>= (897 - exp);
+ }
+ /* Exponent override to SP min exp - 1. */
+ exp = 896;
+ }
+
+ result = sign << 31;
+ result |= extract64(exp, 10, 1) << 30;
+ result |= extract64(exp, 0, 7) << 23;
+ result |= extract64(frac, 29, 23);
+
/* hardware replicates result to both words of the doubleword result. */
return (result << 32) | result;
}
--
1.8.3.1
- [Qemu-devel] [PATCH] ppc: Fix xscvdpspn for SNAN,
Paul A. Clarke <=