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authorPeter Maydell <peter.maydell@linaro.org>2013-12-30 22:57:04 +0000
committerPeter Maydell <peter.maydell@linaro.org>2013-12-31 01:08:57 +0000
commit8c03f27b75a0e3c0f3217aa0f512d9918631b0c1 (patch)
tree545e107c700d21d53c8406021850527b713e06f4
parentfb636ad1694798f96bd2dd188ebb3eb38cd3526a (diff)
downloadqemu-arm-8c03f27b75a0e3c0f3217aa0f512d9918631b0c1.tar.gz
softfloat: Add support for ties-away rounding
IEEE754-2008 specifies a new rounding mode: "roundTiesToAway: the floating-point number nearest to the infinitely precise result shall be delivered; if the two nearest floating-point numbers bracketing an unrepresentable infinitely precise result are equally near, the one with larger magnitude shall be delivered." Implement this new mode (it is needed for ARM). The general principle is that the required code is exactly like the ties-to-even code, except that we do not need to do the "in case of exact tie clear LSB to round-to-even", because the rounding operation naturally causes the exact tie to round up in magnitude. Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
-rw-r--r--fpu/softfloat.c68
-rw-r--r--include/fpu/softfloat.h3
2 files changed, 53 insertions, 18 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 623a4b9257..ce7970f222 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -107,7 +107,7 @@ static int32 roundAndPackInt32( flag zSign, uint64_t absZ STATUS_PARAM)
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = ( roundingMode == float_round_nearest_even );
roundIncrement = 0x40;
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
roundIncrement = 0;
}
@@ -155,7 +155,7 @@ static int64 roundAndPackInt64( flag zSign, uint64_t absZ0, uint64_t absZ1 STATU
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = ( roundingMode == float_round_nearest_even );
increment = ( (int64_t) absZ1 < 0 );
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
increment = 0;
}
@@ -206,7 +206,7 @@ static int64 roundAndPackUint64(flag zSign, uint64_t absZ0,
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = (roundingMode == float_round_nearest_even);
increment = ((int64_t)absZ1 < 0);
- if (!roundNearestEven) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if (roundingMode == float_round_to_zero) {
increment = 0;
} else if (absZ1) {
@@ -354,7 +354,7 @@ static float32 roundAndPackFloat32(flag zSign, int_fast16_t zExp, uint32_t zSig
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = ( roundingMode == float_round_nearest_even );
roundIncrement = 0x40;
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
roundIncrement = 0;
}
@@ -536,7 +536,7 @@ static float64 roundAndPackFloat64(flag zSign, int_fast16_t zExp, uint64_t zSig
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = ( roundingMode == float_round_nearest_even );
roundIncrement = 0x200;
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
roundIncrement = 0;
}
@@ -718,7 +718,7 @@ static floatx80
goto precision80;
}
zSig0 |= ( zSig1 != 0 );
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
roundIncrement = 0;
}
@@ -1029,7 +1029,7 @@ static float128
roundingMode = STATUS(float_rounding_mode);
roundNearestEven = ( roundingMode == float_round_nearest_even );
increment = ( (int64_t) zSig2 < 0 );
- if ( ! roundNearestEven ) {
+ if (!roundNearestEven && roundingMode != float_round_ties_away) {
if ( roundingMode == float_round_to_zero ) {
increment = 0;
}
@@ -1756,6 +1756,11 @@ float32 float32_round_to_int( float32 a STATUS_PARAM)
return packFloat32( aSign, 0x7F, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x7E) {
+ return packFloat32(aSign, 0x7F, 0);
+ }
+ break;
case float_round_down:
return make_float32(aSign ? 0xBF800000 : 0);
case float_round_up:
@@ -1771,8 +1776,9 @@ float32 float32_round_to_int( float32 a STATUS_PARAM)
if ( roundingMode == float_round_nearest_even ) {
z += lastBitMask>>1;
if ( ( z & roundBitsMask ) == 0 ) z &= ~ lastBitMask;
- }
- else if ( roundingMode != float_round_to_zero ) {
+ } else if (roundingMode == float_round_ties_away) {
+ z += lastBitMask >> 1;
+ } else if (roundingMode != float_round_to_zero) {
if ( extractFloat32Sign( make_float32(z) ) ^ ( roundingMode == float_round_up ) ) {
z += roundBitsMask;
}
@@ -3144,6 +3150,9 @@ static float32 roundAndPackFloat16(flag zSign, int_fast16_t zExp,
increment = zSig & (increment << 1);
}
break;
+ case float_round_ties_away:
+ increment = (mask + 1) >> 1;
+ break;
case float_round_up:
increment = zSign ? 0 : mask;
break;
@@ -3449,6 +3458,11 @@ float64 float64_round_to_int( float64 a STATUS_PARAM )
return packFloat64( aSign, 0x3FF, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FE) {
+ return packFloat64(aSign, 0x3ff, 0);
+ }
+ break;
case float_round_down:
return make_float64(aSign ? LIT64( 0xBFF0000000000000 ) : 0);
case float_round_up:
@@ -3465,8 +3479,9 @@ float64 float64_round_to_int( float64 a STATUS_PARAM )
if ( roundingMode == float_round_nearest_even ) {
z += lastBitMask>>1;
if ( ( z & roundBitsMask ) == 0 ) z &= ~ lastBitMask;
- }
- else if ( roundingMode != float_round_to_zero ) {
+ } else if (roundingMode == float_round_ties_away) {
+ z += lastBitMask >> 1;
+ } else if (roundingMode != float_round_to_zero) {
if ( extractFloat64Sign( make_float64(z) ) ^ ( roundingMode == float_round_up ) ) {
z += roundBitsMask;
}
@@ -4722,6 +4737,11 @@ floatx80 floatx80_round_to_int( floatx80 a STATUS_PARAM )
packFloatx80( aSign, 0x3FFF, LIT64( 0x8000000000000000 ) );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FFE) {
+ return packFloatx80(aSign, 0x3FFF, LIT64(0x8000000000000000));
+ }
+ break;
case float_round_down:
return
aSign ?
@@ -4742,8 +4762,9 @@ floatx80 floatx80_round_to_int( floatx80 a STATUS_PARAM )
if ( roundingMode == float_round_nearest_even ) {
z.low += lastBitMask>>1;
if ( ( z.low & roundBitsMask ) == 0 ) z.low &= ~ lastBitMask;
- }
- else if ( roundingMode != float_round_to_zero ) {
+ } else if (roundingMode == float_round_ties_away) {
+ z.low += lastBitMask >> 1;
+ } else if (roundingMode != float_round_to_zero) {
if ( extractFloatx80Sign( z ) ^ ( roundingMode == float_round_up ) ) {
z.low += roundBitsMask;
}
@@ -5801,8 +5822,15 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
if ( (uint64_t) ( z.low<<1 ) == 0 ) z.high &= ~1;
}
}
- }
- else if ( roundingMode != float_round_to_zero ) {
+ } else if (roundingMode == float_round_ties_away) {
+ if (lastBitMask) {
+ add128(z.high, z.low, 0, lastBitMask >> 1, &z.high, &z.low);
+ } else {
+ if ((int64_t) z.low < 0) {
+ ++z.high;
+ }
+ }
+ } else if (roundingMode != float_round_to_zero) {
if ( extractFloat128Sign( z )
^ ( roundingMode == float_round_up ) ) {
add128( z.high, z.low, 0, roundBitsMask, &z.high, &z.low );
@@ -5824,6 +5852,11 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
return packFloat128( aSign, 0x3FFF, 0, 0 );
}
break;
+ case float_round_ties_away:
+ if (aExp == 0x3FFE) {
+ return packFloat128(aSign, 0x3FFF, 0, 0);
+ }
+ break;
case float_round_down:
return
aSign ? packFloat128( 1, 0x3FFF, 0, 0 )
@@ -5846,8 +5879,9 @@ float128 float128_round_to_int( float128 a STATUS_PARAM )
if ( ( ( z.high & roundBitsMask ) | a.low ) == 0 ) {
z.high &= ~ lastBitMask;
}
- }
- else if ( roundingMode != float_round_to_zero ) {
+ } else if (roundingMode == float_round_ties_away) {
+ z.high += lastBitMask>>1;
+ } else if (roundingMode != float_round_to_zero) {
if ( extractFloat128Sign( z )
^ ( roundingMode == float_round_up ) ) {
z.high |= ( a.low != 0 );
diff --git a/include/fpu/softfloat.h b/include/fpu/softfloat.h
index 08c755950d..7f50d4fc03 100644
--- a/include/fpu/softfloat.h
+++ b/include/fpu/softfloat.h
@@ -152,7 +152,8 @@ enum {
float_round_nearest_even = 0,
float_round_down = 1,
float_round_up = 2,
- float_round_to_zero = 3
+ float_round_to_zero = 3,
+ float_round_ties_away = 4,
};
/*----------------------------------------------------------------------------