Category : Files from Magazines
Archive   : DDJ0892.ZIP
Filename : BORL_EXT.ASC

_COMPILER-SPECIFIC C EXTENSIONS_
by Al Stevens

Example 1:

(a)
_AX = 123;
_ES = _DS;

(b)
mov ax,123
push ds
pop es

(c)
mov ax,123
mov ax,ds
mov es,ax

(d)
_ES = _DS;
_AX = 123;

Example 2:

_AH = 0x48; // Allocate memory function
_BX = 10; // # of paragraphs to allocate
geninterrupt(0x21); // call DOS
if ((_FLAGS & 1) == 0) // test carry bit
segment = _AX; // segment of the allocated block
else
// ... error ...

Example 3:

disable();
_SS = oldss; // interrupts must not occur now
_SP = oldsp; // otherwise SS and SP will be wrong
enable();

Example 4:

(a)
void interrupt (*oldISR)(void);
oldISR = getvect(VECTOR);
setvect(VECTOR, newISR);

(b)
(*oldISR)();

(c)
setvect(VECTOR, oldISR);

Example 5:

(a)

typedef struct {
int bp,di,si,ds,es,dx,cx,bx,ax,ip,cs,fl;
} IREGS;



(b)
void interrupt newISR(IREGS ir)
{
// ...
}


(c)

if (ir.ax == 5)
// ....



(d)
ir.ax = 3; // return 3 in ax
ir.fl |= 1; // return the carry bit on


Example 6:

(a)

void interrupt newISR(IREGS ir)
{
// do some processing that might change registers
_AX = ir.ax; // restore the registers that the old ISR needs
_BX = ir.bx;
(*oldISR)(); // chain to the old isr
}



(b)

void interrupt newISR(IREGS ir)
{
(*oldISR)(); // chain to the old isr
ir.ax = _AX; // caller will get ax
ir.fl = _FLAGS; // and the flags
}


(c)

void interrupt newISR(IREGS ir)
{
void interrupt (*tmpISR)();
tmpISR = oldISR; // use function pointer on the stack
_DS = ir.ds; // reset DS
(*tmpISR)(); // chain to the old isr through tmp ptr
}



(d)

void interrupt newISR(IREGS ir)
{
void interrupt (*tmpISR)();
int oldds = _DS; // save ISR's DS
tmpISR = oldISR; // use function pointer on the stack
_DS = ir.ds; // reset DS
(*tmpISR)(); // chain to the old isr through tmp ptr
_DS = oldds; // reset DS
// ... do further processing
}

Example 7:

_data segment para public 'data'
_data ends
_bss segment word public 'bss'
_bss ends
_bssend segment byte public 'bss'
_bssend ends
_stack segment stack 'stack'
_stack ends
_text segment byte public 'code'
_text ends

Example 8:


tsr.exe : tsr.obj emm.obj xms.obj int2f.obj tsrinit.lib
tlink /m /s int2f emm xms tsr,tsr.exe,tsr,$(CLIB) tsrinit

tsrinit.lib : c0t.obj tsrinit.obj emminit.obj xmsinit.obj init.obj
tlib tsrinit +tsrinit.obj +c0t.obj +emminit.obj +xmsinit.obj +init.obj


Example 9:

(a)

if (_CS > 0xa000) {
dispstr("\a\r\nCannot loadhigh");
return;
}



(b)

EXTERN struct vectors {
int vno;
void (interrupt **oldvect)(void);
void (interrupt *newvect)(void);
} vectors[] = {
{TIMER, &oldtimer, (void interrupt (*)())newtimer},
{INT28, &old28, (void interrupt (*)())new28},
{KYBRD, &oldkb, (void interrupt (*)())newkb},
{DISK, &olddisk, (void interrupt (*)())newdisk},
{VIDEO, &oldvideo, (void interrupt (*)())newvideo},
{TSRPLUSINT, &old2f, (void interrupt (*)())new2f},
{0, NULL, NULL}};

#define newvectors(vecs) \
{ \
register struct vectors *vc = vecs; \
while (vc->vno) { \
*(vc->oldvect) = getvect(vc->vno); \
setvect(vc->vno, vc->newvect); \
vc++; \
} \
}

Example 10:

/* ------ compute program size ------- */
highmemory = _CS + ((unsigned)&codeend / 16);
sizeprogram = highmemory - _psp;

/* ------ adjust MCB for TSRPLUS ------- */
_ES = _psp;
_BX = sizeprogram;
_AX = 0x4a00;
geninterrupt(DOS);

Example 11:

(a)

sizeprogram = _CS+((unsigned) main >> 4)-_psp;
if ((unsigned) main % 4)
sizeprogram++;


(b)


_DX = sizeprogram;
_AX = 0x3100;
geninterrupt(DOS);


Example 12:

/* ----- keyboard ISR ------ */
static void interrupt newkb(void)
{
unsigned char kbval = inportb(0x60);
if (!hotkeyhit && !running) {
if (Keymask && (peekb(0, 0x417) & 0xf) == Keymask)
if (Scancode == 0 || Scancode == kbval)
hotkeyhit = TRUE;
if (hotkeyhit) {
/* --- reset the keyboard ---- */
kbval = inportb(0x61);
outportb(0x61, kbval | 0x80);
outportb(0x61, kbval);
outportb(0x20, 0x20);
return;
}
}
(*oldkb)();
}


Example 13:

intsp = _SP;
intss = _SS;
_SP = tsrsp;
_SS = tsrss;