【非典】16 bits to packed BCD, 51 ASM. (计算方法)
【非典】16 bits to packed BCD, 51 ASM. 55周期/93字节(终结）
TEST_NUM EQU 65535
ORG 000H
MOV R2, #LOW(TEST_NUM) ; #11111111B
MOV R3, #HIGH(TEST_NUM); #11111111B ; 65535
CALL BIN2BCD
SJMP $
;==================================
BIN2BCD:
;--------------------------------------*
;Input: R3:R2 --- 16 bits bin |
; R2--Bit 0 to bit 7 |
; R3--Bit 8 to bit 15 |
;Output: R7:R6:R5 --- 5 Dig Packed BCD |
; R5: 个位/十位 |
; R6: 百位/千位 |
; R7: 万位 |
;Usage: PSW (C, AC, OV), Acc, B |
; |
;PS: 55 CYs only. 93 bytes |
; DengMiao 2007-4 Guangzhou |
;--------------------------------------*
MOV A, R2
ANL A, #00000011B
MOV R6, A ; R6 --- *1 (bit 0 to bit 1) (2 bits)
MOV A, R3
RRC A
MOV B, A
MOV A, R2
RRC A
MOV C, B.0
RRC A
MOV R7, A ; R7 --- *4 (bit 2 to bit 10) (8 bits)
MOV A, #25 ; 25 * 4 = 100
XCH A, B
RR A
ANL A, #00111111B
MOV R5, A ; R5 --- *1024 (bit 11 to bit 15) (6 bits)
RL A
ADD A, R5
XCH A, R7 ; R7 == 3 * R5 (<= 3*63=189 < 255)
; A --- *4
;------------------------------
ADD A, R7 ; 4* (A + 3*R5)
JC BIN2BCD_L1
SJMP BIN2BCD_L2
BIN2BCD_L1:
INC R5 ; +1000
ADD A, #6 ; + 24 (4*6)
BIN2BCD_L2:
ADD A, R7 ; 4*(A + 3*R5 + 3*R5)= 4*A + 24*R5
JC BIN2BCD_L1B
SJMP BIN2BCD_L2B
BIN2BCD_L1B:
INC R5 ; +1000
ADD A, #6 ; + 24 (4*6)
BIN2BCD_L2B:
;MOV B, #25
DIV AB ; A 25 (4*25=100)
CJNE A, #10, BIN2BCD_L3 ; A<=25525=10
INC R5 ; *1000
CLR A
BIN2BCD_L3B:
MOV R7, A ; R7 --- *100 Bin/BCD R7<=9
; B --- *4 Bin B <=24
MOV A, #10
XCH A, B ; A --- *4 Bin B <=24
;-------------
;RL A ; A*4
;RL A ; A --- *1 Bin A <=4*24=96
;ORL A, R6 ; R6 --- *1 Bin/BCD R6<=3
; ; A --- *1 Bin A<=96+3=99
;DIV AB
;SWAP A
;ORL A, B
;XCH A, R5 ; R5 --- *1 BCD 个位/十位
; ; A --- *1000 Bin A<=65
;MOV B, #10
;--------------
ADD A, #(BIN2BCD_DB - $ - 3)
MOVC A, @A+PC
ADD A, R6
DA A
XCH A, R5 ; R5 --- *1 BCD 个位/十位
; A --- *1000 Bin A<=65
;--------------------------
DIV AB
XCH A, R7 ; R7 --- *10000 bin/BCD 万位 R7<=6
; A --- *100 Bin/BCD A<=9
; B --- *1000 Bin/BCD B<=9
SWAP A
ORL A, B
SWAP A
MOV R6, A ; R6 --- *100 BCD 百位/千位
RET
BIN2BCD_L3:
SJMP BIN2BCD_L3B
BIN2BCD_DB:
DB 00H, 04H, 08H, 12H, 16H
DB 20H, 24H, 28H, 32H, 36H
DB 40H, 44H, 48H, 52H, 56H
DB 60H, 64H, 68H, 72H, 76H
DB 80H, 84H, 88H, 92H, 96H
;----------END OF BIN2BCD-------
END
算法说明:
把16bits, 分为3段:
X -- Bit 10 到 Bit 15, 共 6 bits; (0 - 63) *1024
Y -- Bit 2 到 Bit 9, 共 8 bits; (0 - 255) *4
Z -- Bit 0 到 Bit 1, 共 2 bits; (0 - 3) *1
可得到:
1024 * X + 4 * Y + Z
= 1000 * X + 24 * X + 4 * Y + Z
= 1000 * X + 4 * ( 6 * X + Y ) + Z
= 1000 * X + 4 * [ Y + (3*X) + (3*X)] + Z
其中 X 的范围为 0 -- 63, 那么(3*X)的范围就为 0 -- 189, <255 (1 byte)
Y+(3*X) 如进位就 X 加1, [Y+(3*X)]-256 加 6, (因为 24 = 4 * 6).
另外, {[Y + (3*x)] - 256}+6 < 255 .
= 1000 * (X+i) + 4 * {[Y + (3*x) + (3*x)] + 6 * i } + Z
= 1000 * (X+i)
+ 100 * {[Y+3*X+3*X+6*i] 25 }
+ 4 * {[Y+3*X+3*X+6*i] MOD 25 } + Z
其中 i 范围为 0 -- 2
{[Y+3*X+3*X+6*i] 25 } <= 10
4 * {[Y+3*X+3*X+6*i] MOD 25 } + Z <= 99
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