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[Xen-devel] [PATCH v6 03/31] 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>
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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