hash.asm

; hash function

org &4000

key1 defb 'SWAP',0
HASH_ADDR equ &8888

ld a,0
ld de, key1
ld hl, &0000

; compute the ascii sum of consecutive memory addresses pointed at the defb instruction. 
ascii_sum:
	  ld a, (de) ; store char for loop control (if A=0 exit)
	  ld (&5555), a  ; move char to temp addr
	  ld bc, (&5555) ; move temp addr char to bc so we can add. 

	  add hl, bc ; sum will be in HL
	  inc de
	  cp 0 
	  jp nz,ascii_sum

; HL should be 013B (SWAP)
; compute the hash by doing ascii_sum MOD 255 (255 will be the length of the hashtable)

ld bc, &ff
;sbc hl, bc 

compute_modulo:
	sbc hl, bc 
	jp nc, compute_modulo 
	jp c, store_hash ; when this jumps, the value in HL will have generated a carry flag, the
                         ; remainder would be at the previous calculation. 
	

; HL should be 3C from the example.
store_hash:

	adc hl, bc ; so we add &ff again to go back. 
	dec hl     ; and add 1 (why the off-by-one here?)
	ld (HASH_ADDR), hl

ret