From 3c85c37f254bdfaea4e105b5014a287b5cf9514b Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Tue, 7 Jan 2014 17:17:50 +0000 Subject: 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 Reviewed-by: Aurelien Jarno Reviewed-by: Richard Henderson --- fpu/softfloat.c | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) (limited to 'fpu') 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; -- cgit v1.2.1