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[base] Significant optimization of `ft_div64by32'

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We shift as many bits as we can into the high register, perform
32-bit division with modulo there, then work through the remaining
bits with long division. This optimization is especially noticeable
for smaller dividends that barely use the high register.

* src/base/ftcalc.c (ft_div64by32): Updated.
This commit is contained in:
Alexei Podtelezhnikov 2014-10-02 23:13:33 -04:00
parent c0ce72a6de
commit 7abdb8ccea
2 changed files with 25 additions and 7 deletions
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13
ChangeLog
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@ -1,3 +1,14 @@
2014-10-02 Alexei Podtelezhnikov <apodtele@gmail.com>
[base] Significant optimization of `ft_div64by32'
We shift as many bits as we can into the high register, perform
32-bit division with modulo there, then work through the remaining
bits with long division. This optimization is especially noticeable
for smaller dividends that barely use the high register.
* src/base/ftcalc.c (ft_div64by32): Updated.
2014-10-02 Dave Arnold <darnold@adobe.com>
[cff] Fix Savannah bug #43271.
@ -70,7 +81,7 @@
Fix Savannah bug #43153.
* src/psaux/psconv.c (PS_Conv_ToFixed): Add protection against
overflow in `divider'.
overflow in `divider'.
2014-09-03 Alexei Podtelezhnikov <apodtele@gmail.com>

19
src/base/ftcalc.c
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@ -304,17 +304,24 @@
FT_Int i;
q = 0;
r = hi;
if ( r >= y )
if ( hi >= y )
return (FT_UInt32)0x7FFFFFFFL;
i = 32;
/* We shift as many bits as we can into the high register, perform */
/* 32-bit division with modulo there, then work through the remaining */
/* bits with long division. This optimization is especially noticeable */
/* for smaller dividends that barely use the high register. */
i = 31 - FT_MSB( hi );
r = ( hi << i ) | ( lo >> ( 32 - i ) ); lo <<= i; /* left 64-bit shift */
q = r / y;
r -= q * y; /* remainder */
i = 32 - i; /* bits remaining in low register */
do
{
q <<= 1;
r = ( r << 1 ) | ( lo >> 31 ); lo <<= 1; /* left 64-bit shift */
r = ( r << 1 ) | ( lo >> 31 ); lo <<= 1;
if ( r >= y )
{