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* softfpu.pp: reverted r28318 and replaced it with a improved solution:

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* Moved handling of 64-bit values > high(int64) to qword_to_float64, so that normalizeRoundAndPackFloat64 procedure stays unmodified compared to C source.
  * Using "jamming" right shift instead of regular one, so the least significant bit is not dropped but participates in rounding.
  * Take a shortcut for values with <= 53 significant bits, which are convertible into float64 exactly and do not need rounding.

git-svn-id: trunk@28346 -
This commit is contained in:
sergei 2014-08-08 20:47:52 +00:00
parent cb470da8d9
commit ee8fcc8bdb
1 changed files with 17 additions and 7 deletions

24
rtl/inc/softfpu.pp
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@ -2868,8 +2868,6 @@ point value corresponding to the abstract input. This routine is just like
`roundAndPackFloat64' except that `zSig' does not have to be normalized.
Bit 63 of `zSig' must be zero, and `zExp' must be 1 less than the ``true''
floating-point exponent.
--
additionally the Pascal version should support Bit 63 set in 'zSig'
----------------------------------------------------------------------------
*}
@ -2878,10 +2876,7 @@ function normalizeRoundAndPackFloat64(zSign: flag; zExp: int16; zSig: bits64): f
shiftCount: int8;
begin
shiftCount := countLeadingZeros64( zSig ) - 1;
if ( shiftCount <= 0) then
result := roundAndPackFloat64( zSign, zExp - shiftCount, zSig shr (-shiftCount))
else
result := roundAndPackFloat64( zSign, zExp - shiftCount, zSig shl shiftCount);
result := roundAndPackFloat64( zSign, zExp - shiftCount, zSig shl shiftCount);
end;
{*
@ -5832,11 +5827,26 @@ End;
*----------------------------------------------------------------------------*}
function qword_to_float64( a: qword ): float64;
{$ifdef fpc}[public,Alias:'QWORD_TO_FLOAT64'];compilerproc;{$endif}
var
shiftCount: int8;
Begin
if ( a = 0 ) then
result := packFloat64( 0, 0, 0 )
else
result := normalizeRoundAndPackFloat64( 0, $43c, a );
begin
shiftCount := countLeadingZeros64(a) - 1;
{ numbers with <= 53 significant bits are converted exactly }
if (shiftCount > 9) then
result := packFloat64(0, $43c - shiftCount, a shl (shiftCount-10))
else if (shiftCount>=0) then
result := roundAndPackFloat64( 0, $43c - shiftCount, a shl shiftCount)
else
begin
{ the only possible negative value is -1, in case bit 63 of 'a' is set }
shift64RightJamming(a, 1, a);
result := roundAndPackFloat64(0, $43d, a);
end;
end;
End;