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[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.

git/fs: mount .git/fs: mount/attach disallowed

--- a/ChangeLog

+++ b/ChangeLog

@@ -1,3 +1,14 @@

+2014-10-02  Alexei Podtelezhnikov  <[email protected]>

+

+	[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  <[email protected]>

 	[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  <[email protected]>

--- a/src/base/ftcalc.c

+++ b/src/base/ftcalc.c

@@ -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 )

       {