32bit to 16bit File Size

File sizes are are often large that 16 bit can handle. On a Floppy disk the are 32bit. The following sample shows one way of solving this issue.

It check if the file size is greater than 64k, if less then the file size is output in bytes. If greater than 64k is output in Kilobytes rounded up to the next kilobyte.

; Provides a 16 bit file size from a 32 bit ; file size up to 1.6Mb maximum, ; anything larger must be treated as ; Megabytes in a similar way. ; The maximum file size shown is 64Mb ; Pass BX = Little Endian ; AX = Big Endian ; Shows either bytes of Kb to nearest whole Kb ; Returns AX=Size, BX=1 is Kb otherwise zero. SubConvertFileSize: CMP AX, 0x0000 ; if AX is NULL = file size < 64k JNE 0x06 MOV AX, BX MOV BX, 0x0000 ; Set 0 for bytes RET SHR BX, 0x08 ; This moves the KB portion into BL ; and makes BH zero MOV BH, AL ; Add the lower half of the big endian SHR BX, 0x02 ; Shift the number down to bit 0 MOV AL, 0x00 ; SHR AH, 0x02 ; Shift 2 more bits from AH into top of AL ADD BH, AL ; Add the extra 2 bytes into BH ADD BX, 0x0001 ; Add 1 for part Kbytes MOV AX, BX MOV BX, 0x0001 ; Set 1 indicating Kilobytes RET

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Last Update 27/12/2022