Last change
on this file since 6099cac was 3ae31e9, checked in by Thomas Lopatic <thomas@…>, 8 years ago |
Imported original source code.
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File size:
918 bytes
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[3ae31e9] | 1 | /*
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| 2 | =============================================================================
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| 3 | ispow2.c -- fast test to see if X is a power of 2
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| 4 | Version 2 -- 1989-01-24 -- D.N. Lynx Crowe
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| 5 |
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| 6 | Returns:
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| 7 |
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| 8 | TRUE if X is a power of 2,
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| 9 | FALSE otherwise.
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| 10 | =============================================================================
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| 11 | */
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| 12 |
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| 13 | #include "stddefs.h"
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| 14 |
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| 15 | short
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| 16 | ispow2(x)
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| 17 | register long x;
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| 18 | {
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| 19 | register short i;
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| 20 | register long k;
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| 21 |
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| 22 | k = 0x00000001L; /* setup the bit mask in k */
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| 23 |
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| 24 | for (i = 32; i--; ) { /* check each bit in x ... */
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| 25 |
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| 26 | if ((x & k) NE 0L) { /* ... for the 1st 1 and ... */
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| 27 |
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| 28 | if ((x & ~k) NE 0L) /* ... if there are others ... */
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| 29 | return(FALSE); /* ... it's not a power of 2 */
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| 30 | else /* ... otherwise .. */
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| 31 | return(TRUE); /* ... it is a power of 2 */
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| 32 | }
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| 33 |
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| 34 | k = k << 1; /* examine the next position */
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| 35 | }
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| 36 |
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| 37 | return(FALSE); /* no bits on isn't a power of 2 */
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| 38 | }
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