mirror of https://github.com/hsoft/collapseos.git
65 lines
1.1 KiB
NASM
65 lines
1.1 KiB
NASM
; *** Requirements ***
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; unsetZ
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;
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; *** Code ***
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; Parse the decimal char at A and extract it's 0-9 numerical value. Put the
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; result in A.
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;
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; On success, the carry flag is reset. On error, it is set.
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parseDecimalDigit:
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; First, let's see if we have an easy 0-9 case
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cp '0'
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ret c ; if < '0', we have a problem
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sub '0' ; our value now is valid if it's < 10
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cp 10 ; on success, C is set, which is the opposite
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; of what we want
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ccf ; invert C flag
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ret
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; Parse string at (HL) as a decimal value and return value in IX under the
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; same conditions as parseLiteral.
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; Sets Z on success, unset on error.
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parseDecimal:
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push hl
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push de
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ld ix, 0
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.loop:
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ld a, (hl)
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or a
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jr z, .end ; success!
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call parseDecimalDigit
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jr c, .error
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; Now, let's add A to IX. First, multiply by 10.
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push ix \ pop de
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add ix, ix ; x2
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jr c, .error
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add ix, ix ; x4
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jr c, .error
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add ix, ix ; x8
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jr c, .error
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add ix, de ; x9
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jr c, .error
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add ix, de ; x10
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jr c, .error
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ld d, 0
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ld e, a
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add ix, de
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jr c, .error
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inc hl
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jr .loop
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cp a ; ensure Z
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jr .end
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.error:
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call unsetZ
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.end:
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pop de
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pop hl
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ret
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