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/***********************************************************************
With non-segmented memory, we just allocate the bitmap as a large 2-D
array. Access to elements is concealed in the macro BITMAP(y,x) which
returns the address of the word at the (y,x) position. On segmented
memory machines (Intel iAPX) this can still be done if the bitmap fits
in one segment, and SEGMEM will have been defined accordingly in
dvixxx.c.
For segmented memories, not all compilers support pointer addressing of
objects larger than a segment, so we implement the bitmap as a vector of
pointers to raster lines, each of which is allocated dynamically.
Element access is again concealed in BITMAP(y,x), but the code has to
ensure that no pointer is ever advanced outside of a raster line. This
affects functions makechar() and prtbmap(). Bitmap access in
dispchar(), fillrect(), and prxbmap() is already restricted to single
raster lines, so no changes are necessary there.
getbmap() handles the necessary allocation for either of these, so
devinit() in each dvixxx remains ignorant of the details.
***********************************************************************/
#if SEGMEM
UNSIGN32* bitmap[YBIT] =
{
(UNSIGN32*)NULL /* only first entry need be initialized */
};
#if (IBM_PC_MICROSOFT & !OS_IBMOS2)
#define BITMAP(y,x) ((UNSIGN32*)normaddr(bitmap[y],(x)<<2))
#define FP_SEG(fp) (*((unsigned *)&(fp) + 1))
#define FP_OFF(fp) (*((unsigned *)&(fp)))
char*
normaddr(p,byte_offset) /* return address p+byte_offset */
char *p;
int byte_offset; /* byte_offset may be positive or negative */
{
long address;
char *q;
/* Reconstruct 32-bit address from SEGMENT*16 + OFFSET + byte_offset */
address = (long)FP_SEG(p); /* long <- unsigned by zero extend */
address <<= 4; /* segment real memory address */
address += (long)FP_OFF(p); /* *p real memory address */
address += (long)byte_offset;/* *(p+byte_offset) real memory address */
/* Renormalize address to OFFSET in 0..15 */
FP_OFF(q) = (unsigned)(address & 0x0f);
FP_SEG(q) = (unsigned)(address >> 4);
return (q);
}
#else /* NOT IBM_PC_MICROSOFT OR OS_IBMOS2 */
#define BITMAP(y,x) (bitmap[y] + (UNSIGN16)(x))
#endif /* IBM_PC_MICROSOFT */
#else /* NOT SEGMEM */
UNSIGN32* bitmap = (UNSIGN32*)NULL;
#define BITMAP(y,x) (bitmap + ((UNSIGN32)XBIT*(UNSIGN32)(y)) + (UNSIGN32)(x))
#endif /* SEGMEM */
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