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; Development testbed for the very simple and ignorant MUL routine
; that is used by q-tris.asm. Uses the routines from decimal.asm for being
; able to print the results.
;
; done by sy2002 in February 2016
#include "../dist_kit/sysdef.asm"
#include "../dist_kit/monitor.def"
.ORG 0x8000
RBRA START, 1
AMOUNT .EQU 22
Factors .DW 0, 0
.DW 0, 1
.DW 1, 0
.DW 0, 60000
.DW 60000, 0
.DW 1, 1
.DW 2, 2
.DW 10, 10
.DW 20, 20
.DW 5, 100
.DW 75, 75 ; 5625
.DW 10000, 1
.DW 1, 10000
.DW 125, 200 ; 25000
.DW 35000, 1
.DW 20, 1900 ; 38000
.DW 1, 39000
.DW 2, 20000
.DW 200, 250 ; 50000
.DW 55000, 1
.DW 1, 58000
.DW 13107, 5 ; 65535
Result_Buffer .BLOCK 5
New_Line .ASCII_W "\n"
START MOVE AMOUNT, R0
MOVE Factors, R1
MOVE New_Line, R2
MOVE 0x30, R3 ; R3 = 0x30 = ASCII "0"
MOVE 5, R4 ; R4 = hardcoded 5 digits
MOVE 1, R5 ; R5 = 1 (for looping)
NEXT_NUM MOVE @R1++, R8 ; retrieve first factor
MOVE @R1++, R9 ; retrieve second factor
RSUB MUL, 1 ; unsigned multiply (low only)
MOVE R10, R8
MOVE Result_Buffer, R9 ; store resulting digits in R9
RSUB MAKE_DECIMAL, 1 ; perform decimal conversion
MOVE R4, R6 ; R6 = 5 digits overall
NEXT_DIGIT MOVE @R9++, R8 ; retrieve digit
ADD R3, R8 ; ASCII conversion
SYSCALL(putc, 1) ; print one digit
SUB R5, R6 ; R6 - 1: all digits done?
RBRA NEXT_DIGIT, !Z ; no: next digit
MOVE R2, R8 ; newline on STDOUT
SYSCALL(puts, 1)
SUB R5, R0 ; R0 - 1: all numbers done?
RBRA NEXT_NUM, !Z
SYSCALL(exit, 1)
; ****************************************************************************
; MUL
; 16-bit integer multiplication, that only calculates the low-word of the
; multiplication, i.e. (factor 1 x factor 2) needs to be smaller than
; 65535, otherwise the result wraps around. The factors as well as the
; result are treated as unsigned.
; Input:
; R8: factor 1
; R9: factor 2
; Output:
; R10: low word of (factor 1 x factor 2)
; ****************************************************************************
MUL INCRB
XOR R10, R10 ; result = 0
CMP R10, R8 ; if factor 1 = 0 ...
RBRA _MUL_RET, Z ; ... then the result is 0
MOVE R8, R0 ; counter for repeated adding
MOVE 1, R1 ; R1 = 1
XOR R2, R2 ; R2 = 0
_MUL_LOOP ADD R9, R10 ; multiply by rep. additions
SUB R1, R0 ; are we done?
RBRA _MUL_COR_OFS, V ; yes due to overflow: return
CMP R2, R0 ; are we done?
RBRA _MUL_RET, Z ; yes due to counter = 0
RBRA _MUL_LOOP, 1
_MUL_COR_OFS SUB R9, R10 ; we added one time too often
_MUL_RET DECRB
RET
; ****************************************************************************
; MAKE_DECIMAL
; 16-bit decimal converter: Input a 16-bit number and receive a 5-element
; list of digits between 0 and 9. Highest decimal at the lowest
; memory address, unused leading decimals are filled with zero.
; No overflow or sanity checks are performed.
; performed.
; R8: 16-bit number
; R9: pointer to the 5-word list that will contain the decimal digits
; ****************************************************************************
MAKE_DECIMAL INCRB
MOVE R8, R6 ; preserve R8 & R9
MOVE R9, R7
MOVE 10, R4 ; R4 = 10
XOR R5, R5 ; R5 = 0
MOVE R9, R0 ; R0: points to result list
ADD 5, R0 ; lowest digit at end of list
_MD_LOOP MOVE R4, R9 ; divide by 10
RSUB DIV_AND_MODULO, 1 ; R8 = "shrinked" dividend
MOVE R9, @--R0 ; extract current digit place
CMP R5, R8 ; done?
RBRA _MD_LOOP, !Z ; no: next iteration
_MD_LEADING_0 CMP R7, R0 ; enough leading "0" there?
RBRA _MD_RET, Z ; yes: return
MOVE 0, @--R0 ; no: add a "0" digit
RBRA _MD_LEADING_0, 1
_MD_RET MOVE R6, R8 ; restore R8 & R9
MOVE R7, R9
DECRB
RET
; ****************************************************************************
; DIV_AND_MODULO
; 16-bit integer division including modulo.
; Ignores the sign of the dividend and the divisor.
; Division by zero yields to an endless loop.
; Input:
; R8: Dividend
; R9: Divisor
; Output:
; R8: Integer quotient
; R9: Modulo
; ****************************************************************************
DIV_AND_MODULO INCRB
XOR R0, R0 ; R0 = 0
CMP R0, R8 ; 0 divided by x = 0 ...
RBRA _DAM_START, !Z
MOVE R0, R9 ; ... and the modulo is 0, too
RBRA _DAM_RET, 1
_DAM_START MOVE R9, R1 ; R1: divisor
MOVE R8, R9 ; R9: modulo
MOVE 1, R2 ; R2 is 1 for speeding up
XOR R8, R8 ; R8: resulting int quotient
_DAM_LOOP ADD R2, R8 ; calculate quotient
SUB R1, R9 ; division by repeated sub.
RBRA _DAM_COR_OFS, V ; wrap around: correct offset
CMP R0, R9
RBRA _DAM_RET, Z ; zero: done and return
RBRA _DAM_LOOP, 1
; correct the values, as we did add 1 one time too much to the
; quotient and subtracted the divisor one time too much from
; the modulo for the sake of having a maxium tight inner loop
_DAM_COR_OFS SUB R2, R8
ADD R1, R9
_DAM_RET DECRB
RET
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