; ============================================================================
; INT 12h - STRING SERVICES
; A library of string functions intended to support programming in assembly,
; or to be used by a higher level language implemented in assembly.
; February 7th, 2026, 10:20AM -- passed all 85 tests on the SD-8516
; ============================================================================
; Function dispatch via AH register:
;   AH=00h: strlen - Get string length
;   AH=01h: strcpy - Copy string
;   AH=02h: strcmp - Compare strings
;   AH=03h: strcat - Concatenate strings
;   AH=04h: atoi - ASCII to integer
;   AH=05h: itoa - Integer to ASCII
;   AH=06h: strupr - Convert to uppercase
;   AH=07h: strlwr - Convert to lowercase
;   AH=08h: strchr - Find character in string
;   AH=09h: strncpy - Copy n characters
;   AH=0Ah: strncmp - Compare n characters
;   AH=0Bh: strcmpi - Compare strings (case-insensitive)
;   AH=0Ch: conv_ch_to_uc - Convert single char to uppercase
;   AH=0Dh: conv_ch_to_lc - Convert single char to lowercase
;   AH=0Eh: test_uc_lc - Test if char is uppercase
;   AH=0Fh: isnum - Test if char is digit (0-9)
;   AH=10h: isalpha - Test if char is letter (A-Z, a-z)
;   AH=11h: puthex - Print byte in AL as hex
;   AH=12h: putbase - Print number in B in base CL
;   AH=13h: print_fld_hex
;   AH=14h: beginswith (Test if string starts with prefix)
;   AH=15h: endswith (Test if string ends with suffix)
;   AH=16h: strstr (Find substring in string)
;   AH=20h: htoi (hex ascii to int)
;   AH=21h: itoh (int to hex ascii)
;
; ============================================================================