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85 lines
1.7 KiB
85 lines
1.7 KiB
SECTION "Utilities", ROM0
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; Busy-wait until vertical blank occurs
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wait_for_vblank::
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ld a, [$ff41]
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and 3
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cp 1
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jr nz, wait_for_vblank
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ret
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; Copy data between two regions (takes 40*N+12 cycles)
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; @param bc Pointer to the destination region
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; @param hl Pointer to the source region
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; @param d Size (in bytes) to copy. Must be >0
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; @destroy a, b, c, d, h, l
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memcpy::
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ld a, [hli] ; 8
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ld [bc], a ; 8
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inc bc ; 8
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dec d ; 4
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jr nz, memcpy ; 12/8
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ret ; 16
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; Copy data between two regions (takes TODO cycles). Only use when size > 255
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; @param bc Pointer to the destination region
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; @param hl Pointer to the source region
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; @param de Size (in bytes) to copy. Must be >0
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; @destroy a, b, c, d, e, h, l
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memcpy16::
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ld a, [hli] ; 8
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ld [bc], a ; 8
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inc bc ; 8
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dec de ; 8
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xor a ; 4
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or d ; 4
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or e ; 4
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jr nz, memcpy16 ; 12/8
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ret ; 16
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; Fill a memory region with a value
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; @param hl Pointer to the destination region
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; @param a Byte to fill with
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; @param c Number of bytes to fill. Must be >0
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; @destroy a, c, hl
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memset::
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ld [hli], a
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dec c
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jr nz, memset
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ret
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; Divide a value by 10 (http://homepage.divms.uiowa.edu/~jones/bcd/decimal.html#division)
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; @param b Dividend
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; @return a Quotient
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; @destroy b
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div10::
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ld a, b
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srl a
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srl a
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add b
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srl a
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add b
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srl a
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srl a
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srl a
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add b
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srl a
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add b
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srl a
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srl a
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srl a
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srl a
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ret
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; Compute the minimum of two unsigned integers
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; @param a First integer
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; @param b Second integer
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; @returns The minimum of the two in A
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; 21 cycles if A < B, 26 cycles otherwise
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min::
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cp b
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ret c
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ld a, b
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ret
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