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fixed: Big::Add sometimes incorrectly rounded the last bit from mantissa 

(when exp_offset == mantissa_size_in_bits ) the rounding_up was always false


git-svn-id: svn://ttmath.org/publicrep/ttmath/trunk@303 e52654a7-88a9-db11-a3e9-0013d4bc506e
This commit is contained in:
Tomasz Sowa 2010-08-18 23:31:58 +00:00
parent c65dac524a
commit 69f065245e
2 changed files with 6 additions and 6 deletions
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11
ttmath/ttmathbig.h
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@ -819,8 +819,7 @@ private:
*/ */
uint AddMantissas( Big<exp, man> & ss2, uint AddMantissas( Big<exp, man> & ss2,
bool & last_bit_set, bool & last_bit_set,
bool & rest_zero, bool & rest_zero)
bool & rounding_up)
{ {
uint c = 0; uint c = 0;
@ -835,8 +834,6 @@ private:
last_bit_set = mantissa.Rcr(1,1); last_bit_set = mantissa.Rcr(1,1);
c += exponent.AddOne(); c += exponent.AddOne();
} }
rounding_up = true;
} }
else else
{ {
@ -890,11 +887,13 @@ public:
if( ss2.IsZero() ) if( ss2.IsZero() )
return 0; return 0;
last_bit_set = rest_zero = do_adding = do_rounding = rounding_up = false; last_bit_set = rest_zero = do_adding = do_rounding = false;
rounding_up = (IsSign() == ss2.IsSign());
AddCheckExponents(ss2, exp_offset, last_bit_set, rest_zero, do_adding, do_rounding); AddCheckExponents(ss2, exp_offset, last_bit_set, rest_zero, do_adding, do_rounding);
if( do_adding ) if( do_adding )
c += AddMantissas(ss2, last_bit_set, rest_zero, rounding_up); c += AddMantissas(ss2, last_bit_set, rest_zero);
if( !round || !last_bit_set ) if( !round || !last_bit_set )
do_rounding = false; do_rounding = false;

1
ttmath/ttmathuint.h
View File

@ -1965,6 +1965,7 @@ public:
this algorithm is described in the following book: this algorithm is described in the following book:
"The art of computer programming 2" (4.3.1 page 272) "The art of computer programming 2" (4.3.1 page 272)
Donald E. Knuth Donald E. Knuth
!! give the description here (from the book)
*/ */
uint Div3(const UInt<value_size> & v, UInt<value_size> * remainder = 0) uint Div3(const UInt<value_size> & v, UInt<value_size> * remainder = 0)
{ {