Difference between revisions of "Z80 Routines:Math:Multiplication"
From WikiTI
(added categorization) |
|||
| Line 7: | Line 7: | ||
They can easily be unrolled to gain some speed. | They can easily be unrolled to gain some speed. | ||
| − | == 8*8 multiplication == | + | == Unsigned versions == |
| + | |||
| + | === 8*8 multiplication === | ||
The following routine multiplies h by e and places the result in hl | The following routine multiplies h by e and places the result in hl | ||
| Line 31: | Line 33: | ||
</nowiki> | </nowiki> | ||
| − | == 16*8 multiplication == | + | === 16*8 multiplication === |
The following routine multiplies de by a and places the result in ahl (which means a is the most significant byte of the product, l the least significant and h the intermediate one...) | The following routine multiplies de by a and places the result in ahl (which means a is the most significant byte of the product, l the least significant and h the intermediate one...) | ||
| Line 59: | Line 61: | ||
</nowiki> | </nowiki> | ||
| − | == 16*16 multiplication == | + | === 16*16 multiplication === |
The following routine multiplies bc by de and places the result in dehl. | The following routine multiplies bc by de and places the result in dehl. | ||
| Line 89: | Line 91: | ||
ret | ret | ||
</nowiki> | </nowiki> | ||
| + | |||
| + | == Signed versions == | ||
| + | |||
| + | <!-- do the routines later, basically try to use cpu instruction that preserve bit 7 (sign) or if this is not possible, just take the sign out, do the multiplication and give the sign afterwards and accordingly. --> | ||
| + | |||
| + | === 8*8 multiplication === | ||
| + | |||
| + | === 16*8 multiplication === | ||
Revision as of 01:47, 9 November 2009
Contents
[hide]Introduction
All these routines use the restoring multiplication algorithm, adapted to the z80 architecture to maximize speed. They can easily be unrolled to gain some speed.
Unsigned versions
8*8 multiplication
The following routine multiplies h by e and places the result in hl
mult_h_e ld l, 0 ld d, l sla h ; optimised 1st iteration jr nc, $+3 ld l, e ld b, 7 _loop: add hl, hl jr nc, $+3 add hl, de djnz _loop ret
16*8 multiplication
The following routine multiplies de by a and places the result in ahl (which means a is the most significant byte of the product, l the least significant and h the intermediate one...)
mult_a_de ld c, 0 ld h, c ld l, h add a, a ; optimised 1st iteration jr nc, $+4 ld h,d ld l,e ld b, 7 _loop: add hl, hl rla jr nc, $+4 add hl, de adc a, c ; yes this is actually adc a, 0 but since c is free we set it to zero and so we can save 1 byte and up to 3 T-states per iteration djnz _loop ret
16*16 multiplication
The following routine multiplies bc by de and places the result in dehl.
mult_de_bc ld h, 0 ld l, h sla e ; optimised 1st iteration rl d jr nc, $+4 ld h, b ld l, c ld a, 15 _loop: add hl, hl rl e rl d jr nc, $+6 add hl, bc jr nc, $+3 inc de dec a jr nz, _loop ret
