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authorPeter Maydell <peter.maydell@linaro.org>2014-01-07 17:17:50 +0000
committerPeter Maydell <peter.maydell@linaro.org>2014-01-08 19:07:22 +0000
commit3c85c37f254bdfaea4e105b5014a287b5cf9514b (patch)
tree672034d2444315ff640bd5d0297d6f0763aa2021 /fpu
parent34e1c27bc3094ffe484d9855e07ad104bddf579f (diff)
downloadqemu-arm-3c85c37f254bdfaea4e105b5014a287b5cf9514b.tar.gz
softfloat: Fix factor 2 error for scalbn on denormal inputs
If the input to float*_scalbn() is denormal then it represents a number 0.[mantissabits] * 2^(1-exponentbias) (and the actual exponent field is all zeroes). This means that when we convert it to our unpacked encoding the unpacked exponent must be one greater than for a normal number, which represents 1.[mantissabits] * 2^(e-exponentbias) for an exponent field e. This meant we were giving answers too small by a factor of 2 for all denormal inputs. Note that the float-to-int routines also have this behaviour of not adjusting the exponent for denormals; however there it is harmless because denormals will all convert to integer zero anyway. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Aurelien Jarno <aurelien@aurel32.net> Reviewed-by: Richard Henderson <rth@twiddle.net>
Diffstat (limited to 'fpu')
-rw-r--r--fpu/softfloat.c29
1 files changed, 21 insertions, 8 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 6312e0c66f..d2e909593f 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -6991,10 +6991,13 @@ float32 float32_scalbn( float32 a, int n STATUS_PARAM )
}
return a;
}
- if ( aExp != 0 )
+ if (aExp != 0) {
aSig |= 0x00800000;
- else if ( aSig == 0 )
+ } else if (aSig == 0) {
return a;
+ } else {
+ aExp++;
+ }
if (n > 0x200) {
n = 0x200;
@@ -7024,10 +7027,13 @@ float64 float64_scalbn( float64 a, int n STATUS_PARAM )
}
return a;
}
- if ( aExp != 0 )
+ if (aExp != 0) {
aSig |= LIT64( 0x0010000000000000 );
- else if ( aSig == 0 )
+ } else if (aSig == 0) {
return a;
+ } else {
+ aExp++;
+ }
if (n > 0x1000) {
n = 0x1000;
@@ -7057,8 +7063,12 @@ floatx80 floatx80_scalbn( floatx80 a, int n STATUS_PARAM )
return a;
}
- if (aExp == 0 && aSig == 0)
- return a;
+ if (aExp == 0) {
+ if (aSig == 0) {
+ return a;
+ }
+ aExp++;
+ }
if (n > 0x10000) {
n = 0x10000;
@@ -7087,10 +7097,13 @@ float128 float128_scalbn( float128 a, int n STATUS_PARAM )
}
return a;
}
- if ( aExp != 0 )
+ if (aExp != 0) {
aSig0 |= LIT64( 0x0001000000000000 );
- else if ( aSig0 == 0 && aSig1 == 0 )
+ } else if (aSig0 == 0 && aSig1 == 0) {
return a;
+ } else {
+ aExp++;
+ }
if (n > 0x10000) {
n = 0x10000;