For Coderz - Small programmers' tricks.

<b>For Coderz</b> - Small programmers' tricks.

           Etudes

             1. Poll keys

    regardless of Caps Lock.


   Suppose you need to interview key "R". In
battery already have some code down
klavishi.No unknown state of Caps Lock.



         OR 32

        CP "r"


   It was so done in ZXUnRar, while
do not have to forcibly make LD
(IY +48), 8 [Caps Lock on], and therefore mask
file name can be entered, without switching
system variables. Similarly, done
check the file extensions and other identifiers that can be 
written in different registers.




             2. Poll keys

        slightly shorter than standard.


   Normal polling cycle through 5, (IY +1) and
variable 23560 (LAST_K) can be reduced:



         LD HL, 23560

         LD A, (HL)

        LD (HL), H; symbol # 5C anyway

                  ; Neklaviaturny


   ... And further validation of keys.

   The computer is ready to receive
the next key. It is important for key
scrolling, etc. (For convenience, scroll
never forget to set the constants
Keyboard REPDEL = # 5C09 and REPPER = # 5C0A.
First it is desirable to equate to 15, the second
- To 1.)


 3. Checking the three-letter extension.


   Very korotkaya.Vyrabotana when optimizing ZXRar, she's in 
ACEdit: 

 goodH3

         PUSH AF

         CP "A

         JR NC, $ +3

         LD A, B

         AND 32

         ADD A, 65

         LD L, A

         POP AF

         CALL etoAN

         JR C, goodH3N

         LD A, B

         CALL etoAN

         JR C, goodH3N

         LD A, H

         CP 32; 2sym

         CALL NZ, etoAN

        RET NC
 goodH3N LD B, 32, H, B

        RET
 etoAN

         CP "0

         RET C

         CP ":

         CCF

         RET NC

         SUB L

         RET C

         ADD A, -26

        RET


   Cause it with the following parameters: A, B, H - symbols of 
the expansion in order. On Output B and H or stored (if 
three-letter extension), or overwritten with spaces (if any 
single character). Criterion harder than Ivan Roshchina: for any

"XAs" exclusion is not made, the name must
include letters of one of a register
and tsifry.Zapreschen tearing probel.Probel
may be at the end (for a 2-character extensions). Names 
beginning with the digits may have a 2 nd and 3 rd marks the 
numbers or letters same registra.Imena, beginning no

with tsifrobukvy, are single-character.



        4. Move to TR-DOS disk.


   Virtually any system program
You can insert a function to delete a file, it
is among the standard Call # 3D13. A
Move among the standard features there, but it
You can call, then do not have to write and
debug terrible algorithm. (No tune, he'll drive the source 
zaporet;)) 

 MOVEDISK

         LD HL, MOVER, (EMCALL +1), HL

        LD C, H

         CALL eM3D13

         LD HL, # 3D13, (EMCALL +1), HL

        JR prcREPR
 MOVER

         LD HL, 5806

        PUSH HL

         LD A, H; -2

         LD (# 5D15), A; NO MSG

         LD (# 5D1F), A; NO LDIR?

        JP 15663


   In this type of procedure (5806, you know) is configured to 
use the driver processing oshibok.U me it is usually a

(Does not support Retry / Abort / Ignore and do not
always stable with No disk, input suppresses
sound off and IM2, the output includes):

 eM3D13

         LD (EMBC +1), BC

         LD (EMBC +4), DE

         LD (EMBC +7), HL

         LD (EMSP +1), SP

        CALL AYOFF; usual jammers AY
 EMREP LD DE, # 5C00, BC, # 400, HL, SYSBUF, SP, HL

         JR NZ, $ +3

         EX DE, HL

        LDIR
 DRV LD A, 0, C, 1

         CALL # 3D13

        LD A, (DRV); PUSH: POP buggy in MOVE

        CP -1

        LD ($ -1), A

         LD C, # 1918

        CALL NZ, # 3D13
 EMBC LD BC, 0, DE, 0, HL, 0

        LD A, 7

        CP C

        JR C, EMCALL

        LD A, 195, (23746), A
EMCALL CALL # 3D13
 EMLDIQ LD HL, (23796)

         PUSH HL

         LD DE, # 5C00, BC, # 400

         LD HL, SYSBUF

         LDIR

         POP HL

        LD (23796), HL
 EMSP LD SP, 0

         LD A, 201, (23746), A

        DI
 EMQq LD DE, IMTAB +256, A, IMER, (DE), A

         DEC D

         LD (DE), A

         INC E

         JR NZ, $ -2

         LD A, D, I, A

         IM 2

         OR A

        RET
POPEMQ POP AF
 EMQ CALL EMQq

         EI

        RET
 ONERR

         EX (SP), HL

         LD A, L

         CP 8020

         JR NZ, EMREP

         CALL 8020

         JR NC, EMSP

         POP HL

        RET



  (In 23747 / 8 should already be addressed ONERR)

   Procedure to 4-kilobyte buffer between the address lying in 
STKEND (23,653 / 4), and register SP. Other subprogrammes TR-DOS

(Eg, delete, and # 18) required a maximum of 257 bytes, not 
counting the stack. With a stack must be measured in each case

as follows: at the end of BASIC area (required
below STKEND, so you need to adjust
STKEND) put some data, which safety check after the disk
operations. When you find the minimum size
stack, it is better to do over his stock in the 16
bytes, because depth of the stack in different versions
TR-DOS is different. For example, ramdisku need a deeper stack, 
because it must determine the current page, and then turn it on 
back. 



  5. Random number in the right range.


   Suppose you have an algorithm for generating
random number from 0 to 255. For example:

[Cut]
I wrote this:

LD HL, (SEED)
LD A, H
AND 31
LD H, A
INC H, L
LD A, (HL)
LD (SEED), HL

You can instead INC H, L fit with the addition of
anything or even multiplication of, say,
5, then slozhenie.Glavnoe, to make sure that
repetition period was larger and the procedure
not long walked in the close-mail addresses (there are 
consecutive zeros, or ff-ki, or text messagi).


Probability numbers will be equal to their frequency in
Rom. If you need a more even distribution, then:

LD HL, (SEED)
LD A, H
AND 31
LD H, A
INC L
LD A, (HL)
INC H
RLCA
XOR (HL)
LD (SEED), HL

And here is the procedure of Wolf2004, independent
from memory (ie, completely predictable when
transfer from computer to computer):

LD HL, (SEED)
LD B, H, C, L
DB "))))
ADD HL, BC
LD BC, 20981
ADD HL, BC
LD (SEED), HL
LD A, H

But only a sequence of type color
squares she does not generate. She was
written for a single value.
[End cut]


   To turn this number into a number, more or less uniform 
distribution between 0 and n-1, better not do so: 



         LD C, n

         SUB C

         JR NC, $ -1

        ADD A, C


   as well:



         ADD A, n

        JR NC, $ -2


   In this council, and is.



         6. Printing messages 8x8.


   Suppose we have a procedure for printing
letters of 8x8. Very often trebuetsya.Naprimer,
is as follows:

 PR88 PUSH DE, HL

         LD H, 0, L, A; if FNT is a multiple of 1024,

         DB ")))"; it is necessary to replace these

         LD BC, FNT; team on the classic

         ADD HL, BC; rlca: l, a, h, 'FNT / 4: db "))

         LD B, 8

         LD A, (HL), (DE), A

         INC L, D

         DJNZ $ -4

         POP HL, DE

         INC E

        RET


   Actually, it can be printed letters of a different size. And 
we need to use it to print, for example, the menu in the 
window, and so that the text was smaller

extra spaces and control codes. More precisely, that there was 
only one control code - 13 (Enter) and terminator - 0.



   Done as follows:

 PRTXTCR LD DE, 0

         LD A, E

         ADD A, 32

         LD E, A

         JR NC, $ +6

         LD A, D

         ADD A, 8

        LD D, A
Behold here the procedure should be called
PRTXT LD (PRTXTCR +1), DE
 PRTXT0 LD A, (HL)

         INC HL

         CP 1913

         JR Z, PRTXTCR

         RET C

         CALL PR88

        JR PRTXT


   Very convenient.

   When you call DE determines the address on the screen upper 
left corner of the window - the beginning Print. Each Enter 
(13) shifts the position Press down on the line, but strictly 
according to the same vertical, where he was the top-left 
corner of the window. 



              7. Register R.


   Add the number to less than 7 bits of register R, to correct 
the register After some delay, so you can:




         LD A, R

         RLCA

         ADD A, the number of * 2

         RRCA

        LD R, A



  8. Conditional compilation (continued).


   If you want to compile
number equal to 0 if metka = 0, and 1 if
metka <> 0 then do not:

IFN metka
metka = 1
ENDIF


   as well:

metka = ~ metka <1 ~ '1


   Where ~ metka understood as ALASM'om
0 ~ + metka, ie metka-1. (If interested,
- ~ Metka, as well as the ~-metka, understood
as-1-metka, and it's shorter to write in the form
metka ~.)

   Comes in handy for creating logical
variables that can be applied in difficult conditions such as 
IFN metka1'metka2. Thus, for example, made in ACEdit.


   A ZASM'ovskoe expression IFUSED replaced by IF ~? Label. 
And, again went talk about It then turns IFDEF IF? label, IFN in

IF, and IF in the IFN.


   By the way, I recommend to save memory
all the tables in the form DB # xx, # yy ... replaced by
DD xxyy ..., and type of DW # xxyy, # zztt ... - By
DD yyxxttzz ...



   PS: Vitamin told to write that comment on the pieces of the 
program is possible through an IF ... ENDIF. I personally use 
IFN 0 ... ENDIF. 

A. Coder