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softfloat: Revert and reimplement remaining portions of 75d62a5856 and 3430b0be36f

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Revert the remaining portions of commits 75d62a5856 and 3430b0be36f
which are under a SoftFloat-2b license, ie the functions
uint64_to_float32() and uint64_to_float64(). (The float64_to_uint64()
and float64_to_uint64_round_to_zero() functions were completely
rewritten in commits fb3ea83aa and 0a87a3107d so can stay.)

Reimplement from scratch the uint64_to_float64() and uint64_to_float32()
conversion functions.

[This is a mechanical squashing together of two separate "revert"
and "reimplement" patches.]

Backports commit 6bb8e0f130bd4aecfe835a0caa94390fa2235fde from qemu
This commit is contained in:
Peter Maydell 2018-02-12 12:52:04 -05:00 committed by Lioncash
parent a9079657e8
commit 5ad42fb01b
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GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 67 additions and 37 deletions
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100
qemu/fpu/softfloat.c
View file

@ -1302,27 +1302,6 @@ float32 int64_to_float32(int64_t a STATUS_PARAM)
}
float32 uint64_to_float32(uint64_t a STATUS_PARAM)
{
int8 shiftCount;
if ( a == 0 ) return float32_zero;
shiftCount = countLeadingZeros64( a ) - 40;
if ( 0 <= shiftCount ) {
return packFloat32(0, 0x95 - shiftCount, (uint32_t)(a<<shiftCount));
}
else {
shiftCount += 7;
if ( shiftCount < 0 ) {
shift64RightJamming( a, - shiftCount, &a );
}
else {
a <<= shiftCount;
}
return roundAndPackFloat32(0, 0x9C - shiftCount, (uint32_t)a STATUS_VAR);
}
}
/*----------------------------------------------------------------------------
| Returns the result of converting the 64-bit two's complement integer `a'
| to the double-precision floating-point format. The conversion is performed
@ -1342,20 +1321,6 @@ float64 int64_to_float64(int64_t a STATUS_PARAM)
}
float64 uint64_to_float64(uint64_t a STATUS_PARAM)
{
int exp = 0x43C;
if (a == 0) {
return float64_zero;
}
if ((int64_t)a < 0) {
shift64RightJamming(a, 1, &a);
exp += 1;
}
return normalizeRoundAndPackFloat64(0, exp, a STATUS_VAR);
}
/*----------------------------------------------------------------------------
| Returns the result of converting the 64-bit two's complement integer `a'
| to the extended double-precision floating-point format. The conversion
@ -1410,6 +1375,71 @@ float128 int64_to_float128(int64_t a STATUS_PARAM)
}
/*----------------------------------------------------------------------------
| Returns the result of converting the 64-bit unsigned integer `a'
| to the single-precision floating-point format. The conversion is performed
| according to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
*----------------------------------------------------------------------------*/
float32 uint64_to_float32(uint64_t a STATUS_PARAM)
{
int shiftcount;
if (a == 0) {
return float32_zero;
}
/* Determine (left) shift needed to put first set bit into bit posn 23
* (since packFloat32() expects the binary point between bits 23 and 22);
* this is the fast case for smallish numbers.
*/
shiftcount = countLeadingZeros64(a) - 40;
if (shiftcount >= 0) {
return packFloat32(0, 0x95 - shiftcount, a << shiftcount);
}
/* Otherwise we need to do a round-and-pack. roundAndPackFloat32()
* expects the binary point between bits 30 and 29, hence the + 7.
*/
shiftcount += 7;
if (shiftcount < 0) {
shift64RightJamming(a, -shiftcount, &a);
} else {
a <<= shiftcount;
}
return roundAndPackFloat32(0, 0x9c - shiftcount, a STATUS_VAR);
}
/*----------------------------------------------------------------------------
| Returns the result of converting the 64-bit unsigned integer `a'
| to the double-precision floating-point format. The conversion is performed
| according to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
*----------------------------------------------------------------------------*/
float64 uint64_to_float64(uint64_t a STATUS_PARAM)
{
int exp = 0x43C;
int shiftcount;
if (a == 0) {
return float64_zero;
}
shiftcount = countLeadingZeros64(a) - 1;
if (shiftcount < 0) {
shift64RightJamming(a, -shiftcount, &a);
} else {
a <<= shiftcount;
}
return roundAndPackFloat64(0, exp - shiftcount, a STATUS_VAR);
}
/*----------------------------------------------------------------------------
| Returns the result of converting the 64-bit unsigned integer `a'
| to the quadruple-precision floating-point format. The conversion is performed
| according to the IEC/IEEE Standard for Binary Floating-Point Arithmetic.
*----------------------------------------------------------------------------*/
float128 uint64_to_float128(uint64_t a STATUS_PARAM)
{
if (a == 0) {

4
qemu/include/fpu/softfloat.h
View file

@ -278,11 +278,11 @@ float64 uint32_to_float64(uint32_t STATUS_PARAM);
floatx80 int32_to_floatx80(int32_t STATUS_PARAM);
float128 int32_to_float128(int32_t STATUS_PARAM);
float32 int64_to_float32(int64_t STATUS_PARAM);
float32 uint64_to_float32(uint64_t STATUS_PARAM);
float64 int64_to_float64(int64_t STATUS_PARAM);
float64 uint64_to_float64(uint64_t STATUS_PARAM);
floatx80 int64_to_floatx80(int64_t STATUS_PARAM);
float128 int64_to_float128(int64_t STATUS_PARAM);
float32 uint64_to_float32(uint64_t STATUS_PARAM);
float64 uint64_to_float64(uint64_t STATUS_PARAM);
float128 uint64_to_float128(uint64_t STATUS_PARAM);
/* We provide the int16 versions for symmetry of API with float-to-int */