diff options
Diffstat (limited to 'utils.h')
| -rw-r--r-- | utils.h | 21 |
1 files changed, 18 insertions, 3 deletions
@@ -27,7 +27,17 @@ static unsigned scaleu(unsigned x, unsigned srcmax, unsigned dstmax); "div bx" /* ax = dx:ax / srcmax */\ __parm [ax] [bx] [cx] \ __value [ax] \ - __modify [ax cx dx] + __modify [ax dx] + +/** Map x linearly from range [0, srcmax] to [0, dstmax]. + * Equivalent of (x * dstmax) / srcmax but with 32-bit signed precision. */ +static int scalei(int x, int srcmax, int dstmax); +#pragma aux scalei = \ + "imul cx" /* dx:ax = x * dstmax */ \ + "idiv bx" /* ax = dx:ax / srcmax */ \ + __parm [ax] [bx] [cx] \ + __value [ax] \ + __modify [ax dx] /** Map x linearly from range [0, srcmax] to [0, dstmax]. * Equivalent of (x * dstmax) / srcmax but with 32-bit signed precision. @@ -36,13 +46,18 @@ static unsigned scaleu(unsigned x, unsigned srcmax, unsigned dstmax); static int scalei_rem(int x, int srcmax, int dstmax, short *rem); #pragma aux scalei_rem = \ "imul cx" /* dx:ax = x * dstmax */ \ + "mov cx, [si]" /* cx = rem */ \ + "test cx, cx" \ + "setns cl" /* cl = 1 if rem positive, 0 if negative */ \ + "movzx cx, cl" \ + "dec cx" /* cx = 0 if rem positive, -1 if negative */ \ "add ax, [si]" /* ax += *rem */ \ - "adc dx, 0" /* dx += 1 if carry */ \ + "adc dx, cx" /* dx += 1 if carry and rem positive, 0 if carry and rem negative (aka. signed addition) */ \ "idiv bx" /* ax = dx:ax / srcmax, dx = new remainder */ \ "mov [si], dx" /* store the new remainder */ \ __parm [ax] [bx] [cx] [si] \ __value [ax] \ - __modify [ax cx dx] + __modify [ax cx dx si] static void bzero(void __far *buf, unsigned int size); #pragma aux bzero = \ |