Data commit

Task/Function-definition/Z80-Assembly/function-definition.z80

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+doMultiply:
+;returns HL = HL times A. No overflow protection.
+push bc
+push de
+    rrca                     ;test if A is odd or even by dividing A by 2.
+    jr c, isOdd
+        ;is even
+
+        ld b,a
+loop_multiplyByEvenNumber:
+        add hl,hl           ;double A until B runs out.
+        djnz loop_multiplyByEvenNumber
+pop de
+pop bc
+ret
+
+isOdd:
+    push hl
+    pop de                  ;de contains original HL. We'll need it later.
+    ld b,a
+loop_multiplyByOddNumber:
+    add hl,hl
+    djnz loop_multiplyByOddNumber
+    add hl,de             ;now add in original HL for the leftover add.
+pop de
+pop bc
+ret