|Z88 Developers' Notes|
12. Integer arithmetic
The Z88 provides multiplication and division routines for 16 and 24 bit binary numbers as well as routines to convert between binary values and decimal numbers represented by ASCII digits. The arithmetic routines use the HL and DE registers (BHL and CDE for 24 bits) as input parameters with the result in HL (or BHL). In the case of division DE (or CDE) returns the remainder. The only error that is flagged is division by zero; Fc = 0 and A = RC_FAIL ($16). No overflow error is provided in the case of multiplication, so it is up to the user of these routines to check for overflow, if necessary.
GN_M16 unsigned 16bit multiplication GN_D16 unsigned 16bit division GN_M24 unsigned 24bit multiplication GN_D24 unsigned 24bit divisionThe conversion routines are quite flexible with the ASCII source or destination being either in memory, at a stream or at a filter. The binary source or destination can either be the BC register pair (16 bits) or a 4 byte buffer in memory (32 bits). When converting from binary to ASCII you have four formatting options. Bits 4 to 7 of the Accumulator (A) define the width of the output field (where zero means as large as is necessary). Bits 1 and 2 of A are set to output a space before and after the decimal digits respectively. If bit 0 of A is set then instead of generating spaces in order to push the number to the right hand edge of the numeric field, zero digits are generated instead.
GN_Gdn convert ASCII string to binary number GN_Pdn convert binary integer to an ASCII stringExample
We now take an opportunity to present a more substantial example than before. The following code fragment accepts a number from the keyboard, converts it to binary, multiplies it by 10, converts back to ASCII decimal and finally outputs it to the screen. Included in this fragment is the memory allocation necessary to obtain an input buffer for the input line routine. Note that some static workspace has to be used here, to store the memory pool handle. This is because an error handler will need to be able to access this handle to close off the memory pool. An error handler associated with this piece of code needs to fetch the memory handle from static workspace and close the memory pool before exciting the application.
include "#memory.def" ; memory call definitions and parameters include "#stdio.def" ; standard I/O call defs. & parameters include "#integer.def" ; integer call definitions include "#errors.def" ; error code calls and definitions; The routine reads a number from the keyboard, multiplies it by 10 and
; first allocate memory
.main call mall ; allocate input buffer call_oz(GN_Nln) ; newline before input xor a ; set options for GN_Sip (empty buffer) ; now get number from keyboard
push iy pop de ; DE = address of input buffer .getline ld b, 6 ; buffer length call_oz(GN_Sip) ; get the ASCII integer jr nc, cont1 ; if no errors then continue cp RC_SUSP ret nz ; exit if some other error ; reposition the cursor before calling GN_Sip again ld a, 13 call_oz(OS_Out) ; output a carriage return ld a, 1 ; option for GN_Sip (buffer has contents) jr getline ; try again
; convert the ASCII number to integer and multiply by 10
.cont1 call_oz(GN_Nln) ; newline push iy pop hl ; HL points at buffer address ld de, 2 ; option for GN_Gdn to store result in BC ld b, 6 ; don't attempt to read more than 6 chars. call_oz(GN_Gdn) ; convert from ASCII decimal to integer ld d,b ld e,c ; result in DE ld hl, 10 ; multiply DE by 10 call_oz(GN_M16) ; multiply... ld b,h ld c,l ; result in BC
; convert and output answer
push iy pop de ; DE points at buffer address xor a ; set convert options (A = 0) call_oz(GN_Pdn) ; convert integer to ASCII decimal ; (convert HL to ASCII decimal at buffer) xor a ld (de),a ; null-terminate string result push iy pop hl ; HL points at start of buffer call_oz(GN_Sop) ; write result to standard output call_oz(GN_Nln)
; now de-allocate memory
push iy pop hl ; address of allocated memory ld c, MS_S2 call_oz(OS_Mgb) ; get current bank binding at segment 2 ld a,b ld bc, size ; size of memory chunk call_oz(OS_Mfr) ; free memory (used for input buffer) ret
; subroutine to allocate memory
.mall ld bc, size ; allocate a whole page (256 bytes) xor a ; as per spec call_oz(OS_Mal) ; allocate memory call_oz(OS_Mpb) ; page the memory into segment 2 push hl pop iy ; IY points at address of allocated memory ret
|Time and date management||Integer arithmetic||Standard Input / Output and the CLI|