base:more_hexadecimal_to_decimal_conversion

These are equivalent routines to Garth Wilson's Hexadecimal to Decimal routines, eliminating the lookup tables in exchange for a little slower execution speed. A discussion of hexadecimal-to-decimal routines can be found in this thread on the 6502.org Forum.

First is the 8-bit version. Start with the input number in accumulator:

; Convert an 8 bit binary value to BCD ; ; This function converts an 8 bit binary value into a 16 bit BCD. It ; works by transferring one bit a time from the source and adding it ; into a BCD value that is being doubled on each iteration. As all the ; arithmetic is being done in BCD the result is a binary to decimal ; conversion. All conversions take 311 clock cycles. ; ; For example the conversion of a $96 would look like this: ; ; BIN = $96 -> BIN' = $2C C = 1 | BCD $0000 x2 + C -> BCD' $0001 ; BIN = $2C -> BIN' = $58 C = 0 | BCD $0001 x2 + C -> BCD' $0002 ; BIN = $58 -> BIN' = $B0 C = 0 | BCD $0002 x2 + C -> BCD' $0004 ; BIN = $B0 -> BIN' = $60 C = 1 | BCD $0004 x2 + C -> BCD' $0009 ; BIN = $60 -> BIN' = $C0 C = 0 | BCD $0009 x2 + C -> BCD' $0018 ; BIN = $C0 -> BIN' = $80 C = 1 | BCD $0018 x2 + C -> BCD' $0037 ; BIN = $80 -> BIN' = $00 C = 1 | BCD $0037 x2 + C -> BCD' $0075 ; BIN = $00 -> BIN' = $00 C = 0 | BCD $0075 x2 + C -> BCD' $0150 ; ; This technique is very similar to Garth Wilsons, but does away with ; the look up table for powers of two and much simpler than the approach ; used by Lance Leventhal in his books (e.g. subtracting out 1000s, 100s, ; 10s and 1s). ; ; Andrew Jacobs, 28-Feb-2004 .ORG $0200 BINBCD8: SED ; Switch to decimal mode LDA #0 ; Ensure the result is clear STA BCD+0 STA BCD+1 LDX #8 ; The number of source bits CNVBIT: ASL BIN ; Shift out one bit LDA BCD+0 ; And add into result ADC BCD+0 STA BCD+0 LDA BCD+1 ; propagating any carry ADC BCD+1 STA BCD+1 DEX ; And repeat for next bit BNE CNVBIT CLD ; Back to binary BRK ; All Done. ; A test value to be converted .ORG $0300 BIN .DB 234 BCD .DS 2

Here a stripped down version to compute a BCD number not larger than 99 (single byte). You send and receive the value in A. The intermediate variables are in page zero.

; Convert a 7 bit binary value to BCD ; ; This routine converts a binary value to BCD; the value cannot be larger than 99. ; Same working principle of the other routines. ; The value to convert is sent in A, and the result will be in A. X value is destroyed. ; The routine executes in 124 cycles (+rts). ; ; Verz!!! 18-Mar-2017 BinBcd_sb ldx #$7 ; The number of source bits 2c asl ; 2c ; ldx #$6 ; you can replace the LDX#$7/ASL with LDX#$6/ASL/ASL ; asl ; to compute values up to 63 (as for a clock) ; asl sta <bin ; 3c lda #$0 ; Ensure the result is clear 2c sed ; Switch to decimal mode 2c CnvBit_sb asl <BIN ; Shift out one bit 5c | sta <BCD0 ; 3c | adc <BCD0 ; 3c | 16c dex ; And repeat for next bit 2c | bne CnvBit_sb ; 3c | cld ; Back to binary 2c rts ; All Done. BIN .equ $fc BCD0 .equ $fb

Here is an equivalent routine for converting 16-bit numbers:

; Convert an 16 bit binary value to BCD ; ; This function converts a 16 bit binary value into a 24 bit BCD. It ; works by transferring one bit a time from the source and adding it ; into a BCD value that is being doubled on each iteration. As all the ; arithmetic is being done in BCD the result is a binary to decimal ; conversion. All conversions take 915 clock cycles. ; ; See BINBCD8 for more details of its operation. ; ; Andrew Jacobs, 28-Feb-2004 .ORG $0200 BINBCD16: SED ; Switch to decimal mode LDA #0 ; Ensure the result is clear STA BCD+0 STA BCD+1 STA BCD+2 LDX #16 ; The number of source bits CNVBIT: ASL BIN+0 ; Shift out one bit ROL BIN+1 LDA BCD+0 ; And add into result ADC BCD+0 STA BCD+0 LDA BCD+1 ; propagating any carry ADC BCD+1 STA BCD+1 LDA BCD+2 ; ... thru whole result ADC BCD+2 STA BCD+2 DEX ; And repeat for next bit BNE CNVBIT CLD ; Back to binary BRK ; All Done. ; A test value to be converted .ORG $0300 BIN .DW 12345 BCD .DS 3

base/more_hexadecimal_to_decimal_conversion.txt · Last modified: 2017-03-18 09:14 by verz