; ============================================================================
  ; 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
  
  ; ============================================================================