diff options
Diffstat (limited to 'sysdeps/sparc')
| -rw-r--r-- | sysdeps/sparc/dotmul.S | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/sysdeps/sparc/dotmul.S b/sysdeps/sparc/dotmul.S new file mode 100644 index 0000000000..1c59a27e80 --- /dev/null +++ b/sysdeps/sparc/dotmul.S @@ -0,0 +1,123 @@ +/* + * Signed multiply, from Appendix E of the Sparc Version 8 + * Architecture Manual. + */ + +/* + * Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the upper 32 bits of + * the 64-bit product). + * + * This code optimizes short (less than 13-bit) multiplies. + */ + +#include "DEFS.h" +FUNC(.mul) + mov %o0, %y ! multiplier -> Y + andncc %o0, 0xfff, %g0 ! test bits 12..31 + be Lmul_shortway ! if zero, can do it the short way + andcc %g0, %g0, %o4 ! zero the partial product and clear N and V + + /* + * Long multiply. 32 steps, followed by a final shift step. + */ + mulscc %o4, %o1, %o4 ! 1 + mulscc %o4, %o1, %o4 ! 2 + mulscc %o4, %o1, %o4 ! 3 + mulscc %o4, %o1, %o4 ! 4 + mulscc %o4, %o1, %o4 ! 5 + mulscc %o4, %o1, %o4 ! 6 + mulscc %o4, %o1, %o4 ! 7 + mulscc %o4, %o1, %o4 ! 8 + mulscc %o4, %o1, %o4 ! 9 + mulscc %o4, %o1, %o4 ! 10 + mulscc %o4, %o1, %o4 ! 11 + mulscc %o4, %o1, %o4 ! 12 + mulscc %o4, %o1, %o4 ! 13 + mulscc %o4, %o1, %o4 ! 14 + mulscc %o4, %o1, %o4 ! 15 + mulscc %o4, %o1, %o4 ! 16 + mulscc %o4, %o1, %o4 ! 17 + mulscc %o4, %o1, %o4 ! 18 + mulscc %o4, %o1, %o4 ! 19 + mulscc %o4, %o1, %o4 ! 20 + mulscc %o4, %o1, %o4 ! 21 + mulscc %o4, %o1, %o4 ! 22 + mulscc %o4, %o1, %o4 ! 23 + mulscc %o4, %o1, %o4 ! 24 + mulscc %o4, %o1, %o4 ! 25 + mulscc %o4, %o1, %o4 ! 26 + mulscc %o4, %o1, %o4 ! 27 + mulscc %o4, %o1, %o4 ! 28 + mulscc %o4, %o1, %o4 ! 29 + mulscc %o4, %o1, %o4 ! 30 + mulscc %o4, %o1, %o4 ! 31 + mulscc %o4, %o1, %o4 ! 32 + mulscc %o4, %g0, %o4 ! final shift + + ! If %o0 was negative, the result is + ! (%o0 * %o1) + (%o1 << 32)) + ! We fix that here. + +#if 0 + tst %o0 + bge 1f + rd %y, %o0 + + ! %o0 was indeed negative; fix upper 32 bits of result by subtracting + ! %o1 (i.e., return %o4 - %o1 in %o1). + retl + sub %o4, %o1, %o1 + +1: + retl + mov %o4, %o1 +#else + /* Faster code adapted from tege@sics.se's code for umul.S. */ + sra %o0, 31, %o2 ! make mask from sign bit + and %o1, %o2, %o2 ! %o2 = 0 or %o1, depending on sign of %o0 + rd %y, %o0 ! get lower half of product + retl + sub %o4, %o2, %o1 ! subtract compensation + ! and put upper half in place +#endif + +Lmul_shortway: + /* + * Short multiply. 12 steps, followed by a final shift step. + * The resulting bits are off by 12 and (32-12) = 20 bit positions, + * but there is no problem with %o0 being negative (unlike above). + */ + mulscc %o4, %o1, %o4 ! 1 + mulscc %o4, %o1, %o4 ! 2 + mulscc %o4, %o1, %o4 ! 3 + mulscc %o4, %o1, %o4 ! 4 + mulscc %o4, %o1, %o4 ! 5 + mulscc %o4, %o1, %o4 ! 6 + mulscc %o4, %o1, %o4 ! 7 + mulscc %o4, %o1, %o4 ! 8 + mulscc %o4, %o1, %o4 ! 9 + mulscc %o4, %o1, %o4 ! 10 + mulscc %o4, %o1, %o4 ! 11 + mulscc %o4, %o1, %o4 ! 12 + mulscc %o4, %g0, %o4 ! final shift + + /* + * %o4 has 20 of the bits that should be in the low part of the + * result; %y has the bottom 12 (as %y's top 12). That is: + * + * %o4 %y + * +----------------+----------------+ + * | -12- | -20- | -12- | -20- | + * +------(---------+------)---------+ + * --hi-- ----low-part---- + * + * The upper 12 bits of %o4 should be sign-extended to form the + * high part of the product (i.e., highpart = %o4 >> 20). + */ + + rd %y, %o5 + sll %o4, 12, %o0 ! shift middle bits left 12 + srl %o5, 20, %o5 ! shift low bits right 20, zero fill at left + or %o5, %o0, %o0 ! construct low part of result + retl + sra %o4, 20, %o1 ! ... and extract high part of result |