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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 multiplicationThe 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_D16 unsigned 16bit division
GN_M24 unsigned 24bit multiplication
GN_D24 unsigned 24bit division
GN_Gdn convert ASCII string to binary numberExample
GN_Pdn convert binary integer to an ASCII string
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; The routine reads a number from the keyboard, multiplies it by 10 and
include "stdio.def" ; standard I/O call defs. & parameters
include "integer.def" ; integer call definitions
include "errors.def" ; error code calls and definitions
; 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
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