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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v8 02/28] xen: Add log2 functionality
From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
log2 helper apis are ported from linux from
commit 13c07b0286d340275f2d97adf085cecda37ede37
(linux/log2.h: Fix rounddown_pow_of_two(1))
Changes made for xen are:
- Only required functionality is retained
- Replace fls_long with flsl
Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
---
v4: - Only retained required functionality
- Replaced fls_long with flsl
- Removed fls_long implementation in bitops.h in v3 version
---
xen/include/xen/log2.h | 167 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 167 insertions(+)
diff --git a/xen/include/xen/log2.h b/xen/include/xen/log2.h
new file mode 100644
index 0000000..86bd861
--- /dev/null
+++ b/xen/include/xen/log2.h
@@ -0,0 +1,167 @@
+/*
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#ifndef _XEN_LOG2_H
+#define _XEN_LOG2_H
+
+#include <xen/types.h>
+#include <xen/bitops.h>
+
+/*
+ * deal with unrepresentable constant logarithms
+ */
+extern __attribute__((const))
+int ____ilog2_NaN(void);
+
+/*
+ * non-constant log of base 2 calculators
+ * - the arch may override these in asm/bitops.h if they can be implemented
+ * more efficiently than using fls() and fls64()
+ * - the arch is not required to handle n==0 if implementing the fallback
+ */
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+ return fls(n) - 1;
+}
+
+static inline __attribute__((const))
+int __ilog2_u64(u64 n)
+{
+ return flsl(n) - 1;
+}
+
+/*
+ * round up to nearest power of two
+ */
+static inline __attribute__((const))
+unsigned long __roundup_pow_of_two(unsigned long n)
+{
+ return 1UL << flsl(n - 1);
+}
+
+/**
+ * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
+ * @n - parameter
+ *
+ * constant-capable log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ *
+ * selects the appropriately-sized optimised version depending on sizeof(n)
+ */
+#define ilog2(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ (n) < 1 ? ____ilog2_NaN() : \
+ (n) & (1ULL << 63) ? 63 : \
+ (n) & (1ULL << 62) ? 62 : \
+ (n) & (1ULL << 61) ? 61 : \
+ (n) & (1ULL << 60) ? 60 : \
+ (n) & (1ULL << 59) ? 59 : \
+ (n) & (1ULL << 58) ? 58 : \
+ (n) & (1ULL << 57) ? 57 : \
+ (n) & (1ULL << 56) ? 56 : \
+ (n) & (1ULL << 55) ? 55 : \
+ (n) & (1ULL << 54) ? 54 : \
+ (n) & (1ULL << 53) ? 53 : \
+ (n) & (1ULL << 52) ? 52 : \
+ (n) & (1ULL << 51) ? 51 : \
+ (n) & (1ULL << 50) ? 50 : \
+ (n) & (1ULL << 49) ? 49 : \
+ (n) & (1ULL << 48) ? 48 : \
+ (n) & (1ULL << 47) ? 47 : \
+ (n) & (1ULL << 46) ? 46 : \
+ (n) & (1ULL << 45) ? 45 : \
+ (n) & (1ULL << 44) ? 44 : \
+ (n) & (1ULL << 43) ? 43 : \
+ (n) & (1ULL << 42) ? 42 : \
+ (n) & (1ULL << 41) ? 41 : \
+ (n) & (1ULL << 40) ? 40 : \
+ (n) & (1ULL << 39) ? 39 : \
+ (n) & (1ULL << 38) ? 38 : \
+ (n) & (1ULL << 37) ? 37 : \
+ (n) & (1ULL << 36) ? 36 : \
+ (n) & (1ULL << 35) ? 35 : \
+ (n) & (1ULL << 34) ? 34 : \
+ (n) & (1ULL << 33) ? 33 : \
+ (n) & (1ULL << 32) ? 32 : \
+ (n) & (1ULL << 31) ? 31 : \
+ (n) & (1ULL << 30) ? 30 : \
+ (n) & (1ULL << 29) ? 29 : \
+ (n) & (1ULL << 28) ? 28 : \
+ (n) & (1ULL << 27) ? 27 : \
+ (n) & (1ULL << 26) ? 26 : \
+ (n) & (1ULL << 25) ? 25 : \
+ (n) & (1ULL << 24) ? 24 : \
+ (n) & (1ULL << 23) ? 23 : \
+ (n) & (1ULL << 22) ? 22 : \
+ (n) & (1ULL << 21) ? 21 : \
+ (n) & (1ULL << 20) ? 20 : \
+ (n) & (1ULL << 19) ? 19 : \
+ (n) & (1ULL << 18) ? 18 : \
+ (n) & (1ULL << 17) ? 17 : \
+ (n) & (1ULL << 16) ? 16 : \
+ (n) & (1ULL << 15) ? 15 : \
+ (n) & (1ULL << 14) ? 14 : \
+ (n) & (1ULL << 13) ? 13 : \
+ (n) & (1ULL << 12) ? 12 : \
+ (n) & (1ULL << 11) ? 11 : \
+ (n) & (1ULL << 10) ? 10 : \
+ (n) & (1ULL << 9) ? 9 : \
+ (n) & (1ULL << 8) ? 8 : \
+ (n) & (1ULL << 7) ? 7 : \
+ (n) & (1ULL << 6) ? 6 : \
+ (n) & (1ULL << 5) ? 5 : \
+ (n) & (1ULL << 4) ? 4 : \
+ (n) & (1ULL << 3) ? 3 : \
+ (n) & (1ULL << 2) ? 2 : \
+ (n) & (1ULL << 1) ? 1 : \
+ (n) & (1ULL << 0) ? 0 : \
+ ____ilog2_NaN() \
+ ) : \
+ (sizeof(n) <= 4) ? \
+ __ilog2_u32(n) : \
+ __ilog2_u64(n) \
+ )
+
+/**
+ * roundup_pow_of_two - round the given value up to nearest power of two
+ * @n - parameter
+ *
+ * round the given value up to the nearest power of two
+ * - the result is undefined when n == 0
+ * - this can be used to initialise global variables from constant data
+ */
+#define roundup_pow_of_two(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ (n == 1) ? 1 : \
+ (1UL << (ilog2((n) - 1) + 1)) \
+ ) : \
+ __roundup_pow_of_two(n) \
+ )
+
+/**
+ * order_base_2 - calculate the (rounded up) base 2 order of the argument
+ * @n: parameter
+ *
+ * The first few values calculated by this routine:
+ * ob2(0) = 0
+ * ob2(1) = 0
+ * ob2(2) = 1
+ * ob2(3) = 2
+ * ob2(4) = 2
+ * ob2(5) = 3
+ * ... and so on.
+ */
+
+#define order_base_2(n) ilog2(roundup_pow_of_two(n))
+#endif /* _XEN_LOG2_H */
--
1.7.9.5
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