lowercase.asm

;{{{ The MIT License
;
;Copyright (c) 2015 Johan Kotlinski
;
;Permission is hereby granted, free of charge, to any person obtaining a copy
;of this software and associated documentation files (the "Software"), to deal
;in the Software without restriction, including without limitation the rights
;to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
;copies of the Software, and to permit persons to whom the Software is
;furnished to do so, subject to the following conditions:
;
;The above copyright notice and this permission notice shall be included in
;all copies or substantial portions of the Software.
;
;THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
;OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
;THE SOFTWARE. }}}

CHAR_TO_LOWERCASE ; ( a -- a )
    sta .save
    sec
    sbc #'a' + $80 
    cmp #1 + 'z' - 'a'
    bcs +
    adc #'a'
    rts
+
.save = * + 1
    lda #0
    sec
    sbc #'A'
    cmp #1 + 'z' - 'a'
    bcs +
    adc #'a'
    rts
+   
    lda .save
    rts