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[Qemu-devel] [PATCH v2 07/24] softfloat: Fix factor 2 error for scalbn o
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH v2 07/24] softfloat: Fix factor 2 error for scalbn on denormal inputs |
Date: |
Mon, 6 Jan 2014 13:11:04 +0000 |
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 <address@hidden>
Reviewed-by: Aurelien Jarno <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
---
fpu/softfloat.c | 29 +++++++++++++++++++++--------
1 file changed, 21 insertions(+), 8 deletions(-)
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 6312e0c..d2e9095 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;
--
1.8.5
- [Qemu-devel] [PATCH v2 15/24] softfloat: Refactor code handling various rounding modes, (continued)
- [Qemu-devel] [PATCH v2 15/24] softfloat: Refactor code handling various rounding modes, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 06/24] softfloat: Only raise Invalid when conversions to int are out of range, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 22/24] target-arm: A64: Add floating-point<->integer conversion instructions, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 23/24] target-arm: A64: Add 1-source 32-to-32 and 64-to-64 FP instructions, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 17/24] target-arm: Prepare VFP_CONV_FIX helpers for A64 uses, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 07/24] softfloat: Fix factor 2 error for scalbn on denormal inputs,
Peter Maydell <=
- [Qemu-devel] [PATCH v2 20/24] target-arm: A64: Add extra VFP fixed point conversion helpers, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 16/24] softfloat: Add support for ties-away rounding, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 10/24] softfloat: Fix float64_to_uint32, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 12/24] softfloat: Provide complete set of accessors for fp state, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 03/24] softfloat: Add 16 bit integer to float conversions, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 09/24] softfloat: Fix float64_to_uint64_round_to_zero, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 11/24] softfloat: Fix float64_to_uint32_round_to_zero, Peter Maydell, 2014/01/06
- [Qemu-devel] [PATCH v2 18/24] target-arm: Rename A32 VFP conversion helpers, Peter Maydell, 2014/01/06