Simple String Comparisons by Jonathyn Bet'nct
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Simple String Comparisons

These two routines will compare two strings, in Pascal string format (length byte followed by string). Upon entry, the addresses of the strings are stored in $FA/FB and $FC/FD. $FF is used as a temporary variable. Upon exit, the zero flag is set if the strings are equal, and cleared otherwise; thus BEQ and BNE can be used. High ASCII characters are considered the same as their low ASCII equivalents; to differentiate between high and low ASCII, simply remove the AND #$7F's.

Comparing Strings (Case-Sensitive):

STREQU:     LDY #$00        ;Compare strings, case-sensitive
            LDA ($FA),Y     ;Naturally, the zero flag is used to return if the strings are equal
            CMP ($FC),Y
            BEQ STREQU1
            RTS
STREQU1:    TAY
STREQULP:   LDA ($FC),Y
            AND #$7F
            STA $FF
            LDA ($FA),Y
            AND #$7F
            CMP $FF
            BNE STREQUEX
            DEY
            BNE STREQULP
STREQUEX:   RTS

Comparing Strings (Case-Insensitive):

STREQI:     LDY #$00        ;Compare strings, case-insensitive
            LDA ($FA),Y     ;Naturally, the zero flag is used to return if the strings are equal
            CMP ($FC),Y
            BEQ STREQI1
            RTS
STREQI1:    TAY
STREQILP:   LDA ($FC),Y
            AND #$7F
            CMP #$7B
            BCS STREQI2
            CMP #$61
            BCC STREQI2
            SBC #$20
STREQI2:    STA $FF
            LDA ($FA),Y
            AND #$7F
            CMP #$7B
            BCS STREQI3
            CMP #$61
            BCC STREQI3
            SBC #$20
STREQI3:    CMP $FF
            BNE STREQIEX
            DEY
            BNE STREQILP
STREQIEX:   RTS