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DAA & DAS algorithms in ARM assembly
This commit is contained in:
Aaron Culliney
parent
d517339842
commit
792c0a0b08
167
src/arm/cpu.S
167
src/arm/cpu.S
@ -782,60 +782,48 @@
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ADd memory to accumulator with Carry
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---------------------------------- */
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#define _AF r10
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#define hi_nib r0
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#define lo_nib r9
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#define carry r9
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#define lo_nyb r1
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// Decimal mode
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ENTRY(op_ADC_dec)
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IncOpCycles
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GetFromEA_B
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DebugBCDCheck
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// initial addition with nybble carry check
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and _AF, A_Reg, #0x10
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bt
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adcs r0, A_Reg, r0
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and r1, A_Reg, #0x10
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eor _AF, _AF, r1
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// DAA algorithm : http://www.ray.masmcode.com/BCDdaa.html
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// CF_old = CF
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// IF (al AND 0Fh > 9) or (the Auxilliary Flag is set)
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// al = al + 6
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// CF = CF (automagically) or CF_old
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// AF set (automagically)
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// ENDIF
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// IF (al > 99h) or (Carry Flag is set)
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// al = al + 60h
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// CF set
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// ENDIF
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lahf
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// isolate lo nybbles
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mov lo_nyb, A_Reg
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mov r9, r0
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and lo_nyb, lo_nyb, #0x0F
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and r9, r9, #0x0F
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// lo nybble addition with carry
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tst F_Reg, #C_Flag
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addne r9, r9, #1
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add lo_nyb, lo_nyb, r9
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// prep 65c02 flags
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bic F_Reg, #NVZC_Flags
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mov r1, r0
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and r1, r1, #0x0f
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cmp r1, #0x09
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bhi _daa_lo_nyb
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teq _AF, #0
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beq _daa_next0
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_daa_lo_nyb: mov r0, r0, LSL #24
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adds r0, r0, #0x06000000 // adjust lo nybble
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mov r0, r0, LSR #24
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bcs _daa_hi_nyb
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_daa_next0: tst arm_flags, #C_Flag
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bne _daa_hi_nyb
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cmp r0, #0x9A
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bmi _daa_next1
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_daa_hi_nyb: add r0, r0, #0x60 // adjust hi nybble
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orr F_Reg, F_Reg, #C_Flag // FlagC
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_daa_next1: tst r0, #0x80
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beq _daa_next2
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orr F_Reg, F_Reg, #N_Flag // FlagN
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_daa_next2: tst r0, #0xFF
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bne _daa_finish
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orr F_Reg, F_Reg, #Z_Flag // FlagZ
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_daa_finish: mov A_Reg, r0
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// lo nybble DAA (Decimal Adjustment after Addition), saving carry (+0, +1, +2)
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cmp lo_nyb, #0x09
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addhi lo_nyb, lo_nyb, #6
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mov carry, lo_nyb, LSR #4
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and lo_nyb, lo_nyb, #0x0F
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// isolate hi nybbles
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mov A_Reg, A_Reg, LSR #4
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mov r0, r0, LSR #4
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// hi nybble addition with carry
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add r0, r0, carry
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add r0, A_Reg, r0
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// hi nybble DAA
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cmp r0, #0x09
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addhi r0, #6
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orrhi F_Reg, #C_Flag
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// merge nybbles
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mov r0, r0, LSL #4
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orr A_Reg, r0, lo_nyb
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// NZ flags
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tst A_Reg, #0x80
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orrne F_Reg, F_Reg, #N_Flag
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tst A_Reg, #0xFF
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orreq F_Reg, F_Reg, #Z_Flag
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Continue
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#define maybe_DoADC_d \
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@ -1964,55 +1952,52 @@ ENTRY(op_RTS) // 0x60
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SBC instructions
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SuBtract memory from accumulator with Borrow
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---------------------------------- */
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#define borrow carry
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ENTRY(op_SBC_dec)
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IncOpCycles
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GetFromEA_B
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DebugBCDCheck
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// initial subtraction with nybble borrow check
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and _AF, A_Reg, #0x10
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btc
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/*cmc*/
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sbcs r0, A_Reg, r0
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and r1, A_Reg, #0x10
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eor _AF, _AF, r1
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// DAS algorithm : http://www.ray.masmcode.com/BCDdas.html
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// CF_old = CF
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// IF (al AND 0Fh > 9) or (the Auxilliary Flag is set)
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// al = al - 6
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// CF = CF (automagically) or CF_old
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// AF set (automagically)
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// ENDIF
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// IF (al > 99h) or (Carry Flag is set)
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// al = al - 60h
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// ^CF set
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// ENDIF
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lahf
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bic F_Reg, F_Reg, #NVZ_Flags
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// isolate lo nybbles
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mov lo_nyb, A_Reg
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mov r9, r0
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and lo_nyb, lo_nyb, #0x0F
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and r9, r9, #0x0F
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// lo nybble subtraction with borrow
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sub lo_nyb, lo_nyb, r9
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and lo_nyb, lo_nyb, #0xFF
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tst F_Reg, #C_Flag
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subeq lo_nyb, lo_nyb, #1
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andeq lo_nyb, lo_nyb, #0xFF
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// prep 65c02 flags
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bic F_Reg, #NVZC_Flags
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orr F_Reg, #C_Flag
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mov r1, r0
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and r1, r1, #0x0f
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cmp r1, #0x09
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bhi _das_lo_nyb
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teq _AF, #0
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beq _das_next0
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_das_lo_nyb: sbcs r0, r0, #0x06000000 // adjust lo nybble
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bcs _das_hi_nyb
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_das_next0: tst arm_flags, #C_Flag
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bne _das_hi_nyb
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cmp r0, #0x9A
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bmi _das_next1
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_das_hi_nyb: sub r0, r0, #0x60 // adjust hi nybble
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bic F_Reg, F_Reg, #C_Flag // !FlagC
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_das_next1: tst r0, #0x80
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beq _das_next2
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orr F_Reg, F_Reg, #N_Flag // FlagN
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_das_next2: tst r0, #0xFF
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bne _das_finish
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orr F_Reg, F_Reg, #Z_Flag // FlagZ
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_das_finish: mov A_Reg, r0
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// lo nybble DAS (Decimal Adjustment after Subtraction), saving borrow
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eor borrow, borrow, borrow
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cmp lo_nyb, #0x09
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movhi borrow, #1
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subhi lo_nyb, lo_nyb, #6
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andhi lo_nyb, lo_nyb, #0x0F
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// isolate hi nybbles
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mov A_Reg, A_Reg, LSR #4
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mov r0, r0, LSR #4
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// hi nybble subtraction with borrow
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sub r0, A_Reg, r0
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and r0, r0, #0xFF
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sub r0, r0, borrow
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and r0, r0, #0xFF
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// hi nybble DAS
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cmp r0, #0x09
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subhi r0, #6
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bichi F_Reg, #C_Flag
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andhi r0, r0, #0x0F
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// merge nybbles
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mov r0, r0, LSL #4
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orr A_Reg, r0, lo_nyb
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// NZ flags
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tst A_Reg, #0x80
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orrne F_Reg, F_Reg, #N_Flag
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tst A_Reg, #0xFF
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orreq F_Reg, F_Reg, #Z_Flag
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Continue
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#define maybe_DoSBC_d \
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@ -539,7 +539,7 @@ ENTRY(op_ADC_dec)
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#else
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// DAA algorithm : http://www.ray.masmcode.com/BCDdaa.html
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// CF_old = CF
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// IF (al AND 0Fh > 9) or (the Auxilliary Flag is set)
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// IF (al AND 0Fh > 9) or (the Auxiliary Flag is set)
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// al = al + 6
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// CF = CF (automagically) or CF_old
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// AF set (automagically)
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@ -1727,7 +1727,7 @@ ENTRY(op_SBC_dec)
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sbbb A_Reg, %al
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// DAS algorithm : http://www.ray.masmcode.com/BCDdas.html
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// CF_old = CF
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// IF (al AND 0Fh > 9) or (the Auxilliary Flag is set)
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// IF (al AND 0Fh > 9) or (the Auxiliary Flag is set)
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// al = al - 6
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// CF = CF (automagically) or CF_old
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// AF set (automagically)
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