MRAB wrote:
Later processors have a DAS instruction, which is used after BCD
subtraction.
The humble 6502 doesn't have DAA/DAS, but instead has a decimal mode flag.
The 68000 also had a Decimal Add instruction, but disappointingly
it only worked a byte at a time. I guess running COBOL at high
speed wasn't a priority by then.
But for sheer unadulterated decimalness, you can't beat the
custom CPU that HP used in their handheld calculators in the
70s and 80s. Early versions of it did *only* decimal arithmetic
(on 14-digit registers and memory locations). An option for
binary wasn't added until the HP-41.
--
Greg
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