diff options
Diffstat (limited to 'utils.h')
| -rw-r--r-- | utils.h | 19 |
1 files changed, 14 insertions, 5 deletions
@@ -60,7 +60,17 @@ static unsigned scaleu(unsigned x, unsigned srcmax, unsigned dstmax); "div bx" /* ax = dx:ax / srcmax */\ __parm [ax] [bx] [cx] \ __value [ax] \ - __modify [ax dx] + __modify exact [ax dx] + +/** Map x linearly from range [0, srcmax] to [0, 2^dstmax]. + * Equivalent to above, but uses shift instead of division. */ +static unsigned scaleu_shift(unsigned x, unsigned char srcmax, unsigned dstmax); +#pragma aux scaleu_shift = \ + "mul dx" /* dx:ax = x * dstmax */ \ + "shrd ax, dx, cl" /* ax = dx:ax / 2^srcmax */ \ + __parm [ax] [cl] [dx] \ + __value [ax] \ + __modify exact [ax dx] /** Map x linearly from range [0, srcmax] to [0, dstmax]. * Equivalent of (x * dstmax) / srcmax but with 32-bit signed precision. */ @@ -70,12 +80,11 @@ static int scalei(int x, int srcmax, int dstmax); "idiv bx" /* ax = dx:ax / srcmax */ \ __parm [ax] [bx] [cx] \ __value [ax] \ - __modify [ax dx] + __modify exact [ax dx] /** Map x linearly from range [0, srcmax] to [0, dstmax]. - * Equivalent of (x * dstmax) / srcmax but with 32-bit signed precision. - * Division remainder is returned in rem, which should be reused - * in future calls to reduce rounding error. */ + * Equivalent to scalei, but the division remainder is returned in rem, + * which can be reused in future calls to reduce rounding error. */ static int scalei_rem(int x, int srcmax, int dstmax, short *rem); #pragma aux scalei_rem = \ "imul cx" /* dx:ax = x * dstmax */ \ |