[Qemu-devel] [PATCH] target-arm: Squash input denormals in FRECPS and FRSQRTS

[Peter Maydell]

The helper functions for FRECPS and FRSQRTS have special case
handling that includes checks for zero inputs, so squash input
denormals if necessary before those checks. This fixes incorrect
output when the FPCR DZ bit is set to enable squashing of input
denormals.

Signed-off-by: Peter Maydell <address@hidden>
---
A quick eyeball of helper-a64.c suggests that these are the only
other insns we needed to fix, and a risu test of these insns
confirms that (a) they're buggy and (b) this patch fixes them.
I haven't done an exhaustive coverage test of the whole instruction
set with the DZ bit set, though...

 target-arm/helper-a64.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/target-arm/helper-a64.c b/target-arm/helper-a64.c
index ebd9247..8aa40e9 100644
--- a/target-arm/helper-a64.c
+++ b/target-arm/helper-a64.c
@@ -229,6 +229,9 @@ float32 HELPER(recpsf_f32)(float32 a, float32 b, void 
*fpstp)
 {
     float_status *fpst = fpstp;
 
+    a = float32_squash_input_denormal(a, fpst);
+    b = float32_squash_input_denormal(b, fpst);
+
     a = float32_chs(a);
     if ((float32_is_infinity(a) && float32_is_zero(b)) ||
         (float32_is_infinity(b) && float32_is_zero(a))) {
@@ -241,6 +244,9 @@ float64 HELPER(recpsf_f64)(float64 a, float64 b, void 
*fpstp)
 {
     float_status *fpst = fpstp;
 
+    a = float64_squash_input_denormal(a, fpst);
+    b = float64_squash_input_denormal(b, fpst);
+
     a = float64_chs(a);
     if ((float64_is_infinity(a) && float64_is_zero(b)) ||
         (float64_is_infinity(b) && float64_is_zero(a))) {
@@ -253,6 +259,9 @@ float32 HELPER(rsqrtsf_f32)(float32 a, float32 b, void 
*fpstp)
 {
     float_status *fpst = fpstp;
 
+    a = float32_squash_input_denormal(a, fpst);
+    b = float32_squash_input_denormal(b, fpst);
+
     a = float32_chs(a);
     if ((float32_is_infinity(a) && float32_is_zero(b)) ||
         (float32_is_infinity(b) && float32_is_zero(a))) {
@@ -265,6 +274,9 @@ float64 HELPER(rsqrtsf_f64)(float64 a, float64 b, void 
*fpstp)
 {
     float_status *fpst = fpstp;
 
+    a = float64_squash_input_denormal(a, fpst);
+    b = float64_squash_input_denormal(b, fpst);
+
     a = float64_chs(a);
     if ((float64_is_infinity(a) && float64_is_zero(b)) ||
         (float64_is_infinity(b) && float64_is_zero(a))) {
-- 
1.9.1