fpu/softfloat: Don't set Invalid for float-to-int(MAXINT)

[Qemu-devel] [PATCH] fpu/softfloat: Don't set Invalid for float-to-int(MAXINT)

Peter Maydell posted 1 patch 7 years, 5 months ago

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git fetch https://github.com/patchew-project/qemu tags/patchew/20180510140141.12120-1-peter.maydell@linaro.org

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fpu/softfloat.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

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[Qemu-devel] [PATCH] fpu/softfloat: Don't set Invalid for float-to-int(MAXINT)

Posted by Peter Maydell 7 years, 5 months ago

In float-to-integer conversion, if the floating point input
converts exactly to the largest or smallest integer that
fits in to the result type, this is not an overflow.
In this situation we were producing the correct result value,
but were incorrectly setting the Invalid flag.
For example for Arm A64, "FCVTAS w0, d0" on an input of
0x41dfffffffc00000 should produce 0x7fffffff and set no flags.

Fix the boundary case to take the right half of the if()
statements.

This fixes a regression from 2.11 introduced by the softfloat
refactoring.

Cc: qemu-stable@nongnu.org
Fixes: ab52f973a50
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 fpu/softfloat.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 8401b37bd4..9bcaaebe4f 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1368,14 +1368,14 @@ static int64_t round_to_int_and_pack(FloatParts in, int rmode,
             r = UINT64_MAX;
         }
         if (p.sign) {
-            if (r < -(uint64_t) min) {
+            if (r <= -(uint64_t) min) {
                 return -r;
             } else {
                 s->float_exception_flags = orig_flags | float_flag_invalid;
                 return min;
             }
         } else {
-            if (r < max) {
+            if (r <= max) {
                 return r;
             } else {
                 s->float_exception_flags = orig_flags | float_flag_invalid;
-- 
2.17.0

Re: [Qemu-devel] [PATCH] fpu/softfloat: Don't set Invalid for float-to-int(MAXINT)

Posted by Richard Henderson 7 years, 5 months ago

On 05/10/2018 07:01 AM, Peter Maydell wrote:
> In float-to-integer conversion, if the floating point input
> converts exactly to the largest or smallest integer that
> fits in to the result type, this is not an overflow.
> In this situation we were producing the correct result value,
> but were incorrectly setting the Invalid flag.
> For example for Arm A64, "FCVTAS w0, d0" on an input of
> 0x41dfffffffc00000 should produce 0x7fffffff and set no flags.
> 
> Fix the boundary case to take the right half of the if()
> statements.
> 
> This fixes a regression from 2.11 introduced by the softfloat
> refactoring.
> 
> Cc: qemu-stable@nongnu.org
> Fixes: ab52f973a50
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  fpu/softfloat.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~