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Add __constant_flsl(), because it's useful for finding out the next

power-of-two up from a given constant via
  ( 1 << fls ( constant - 1 ) )

fls(), flsl(), ffs() and ffsl() appear in strings.h according to
POSIX.
tags/v0.9.3
Michael Brown 18年前
コミット
2f0d412210
1個のファイルの変更54行の追加0行の削除
  1. 54
    0
      src/include/strings.h

+ 54
- 0
src/include/strings.h ファイルの表示

@@ -0,0 +1,54 @@
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+#ifndef _STRINGS_H
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+#define _STRINGS_H
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+
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+#include <limits.h>
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+
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+static inline __attribute__ (( always_inline )) int
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+__constant_flsl ( unsigned long x ) {
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+	int r = 0;
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+
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+#if ULONG_MAX > 0xffffffff
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+	if ( x & 0xffffffff00000000UL ) {
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+		x >>= 32;
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+		r += 32;
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+	}
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+#endif
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+	if ( x & 0xffff0000UL ) {
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+		x >>= 16;
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+		r += 16;
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+	}
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+	if ( x & 0xff00 ) {
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+		x >>= 8;
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+		r += 8;
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+	}
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+	if ( x & 0xf0 ) {
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+		x >>= 4;
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+		r += 4;
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+	}
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+	if ( x & 0xc ) {
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+		x >>= 2;
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+		r += 2;
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+	}
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+	if ( x & 0x2 ) {
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+		x >>= 1;
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+		r += 1;
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+	}
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+	if ( x & 0x1 ) {
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+		r += 1;
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+	}
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+	return r;
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+}
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+
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+#define __constant_fls(x) __constant_flsl(x)
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+
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+/* We don't actually have these functions yet */
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+extern int __fls ( int x );
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+extern int __flsl ( long x );
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+
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+#define flsl( x ) \
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+	( __builtin_constant_p ( x ) ? __constant_flsl ( x ) : __flsl ( x ) )
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+
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+#define fls( x ) \
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+	( __builtin_constant_p ( x ) ? __constant_fls ( x ) : __fls ( x ) )
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+
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+#endif /* _STRINGS_H */

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