HP SunSoft Pascal 4.0 - Manual (Page 134)

110 Pascal 4.0 User’s Guide
6
Pascal Set Type
In Pascal, a set type is implemented as a bit vector, which is similar to a C
short-word array. Direct access to individual elements of a set is highly
machine-dependent and should be avoided.
In Pascal, bits are numbered within a byte from the most significant to least, as
shown in Table 6-3.
In C, a set could be described as a short-word array beginning at an even
address. With the current set representation, it does not matter what the
lower-bound value is.
The nth element in a set [lower...upper] can be tested as follows:
Table 6-3 Set Implementation
Set Bit Numbering
set+3: 31, 30, 29, 28, 27, 26, 25, 24
set+2: 23, 22, 21, 20, 19, 18, 17, 16
set+1: 15, 14, 13, 12, 11, 10, 9, 8
set+0: 7, 6, 5, 4, 3, 2, 1, 0
#define LG2BITSLONG 5 /* log2( bits in long word) */
#define LG2BITSWORD 4 /* log2( bits in short word) */
#define MSKBITSLONG 0x1f
#define MSKBITSHORT 0x0
short *setptr; /* set as array of shorts */
int upper; /* upper bound of the set */
int elem; /* ordinal value of set element */
int i;
if ( setptr[elem >> LG2BITSWORD] &
(1 << (elem & MSKBITSWORD)) ) {
/* elem is in set */
}