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Message-Id: <20060913175940.21216.63597.stgit@warthog.cambridge.redhat.com>
Date: Wed, 13 Sep 2006 18:59:40 +0100
From: David Howells <dhowells@...hat.com>
To: torvalds@...l.org, akpm@...l.org
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
dhowells@...hat.com
Subject: [PATCH 4/7] Implement a general integer log2 facility in the kernel [try #2]
From: David Howells <dhowells@...hat.com>
This facility provides three entry points:
ilog2() Log base 2 of unsigned long
ilog2_u32() Log base 2 of u32
ilog2_u64() Log base 2 of u64
These facilities can either be used inside functions on dynamic data:
int do_something(long q)
{
...;
y = ilog2(x)
...;
}
Or can be used to statically initialise global variables with constant values:
unsigned n = ilog2(27);
When performing static initialisation, the compiler will report "error:
initializer element is not constant" if asked to take a log of zero or of
something not reducible to a constant. They treat negative numbers as
unsigned.
When not dealing with a constant, they fall back to using fls() which permits
them to use arch-specific log calculation instructions - such as BSR on
x86/x86_64 or SCAN on FRV - if available.
Signed-Off-By: David Howells <dhowells@...hat.com>
---
fs/ext2/super.c | 6 -
fs/ext3/super.c | 6 -
include/asm-frv/bitops.h | 44 +++++++++++
include/linux/kernel.h | 9 --
include/linux/log2.h | 188 ++++++++++++++++++++++++++++++++++++++++++++++
mm/page_alloc.c | 4 -
6 files changed, 239 insertions(+), 18 deletions(-)
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 681dea8..b4b4eae 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -548,8 +548,6 @@ static int ext2_check_descriptors (struc
return 1;
}
-#define log2(n) ffz(~(n))
-
/*
* Maximal file size. There is a direct, and {,double-,triple-}indirect
* block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
@@ -784,9 +782,9 @@ static int ext2_fill_super(struct super_
sbi->s_sbh = bh;
sbi->s_mount_state = le16_to_cpu(es->s_state);
sbi->s_addr_per_block_bits =
- log2 (EXT2_ADDR_PER_BLOCK(sb));
+ ilog2 (EXT2_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits =
- log2 (EXT2_DESC_PER_BLOCK(sb));
+ ilog2 (EXT2_DESC_PER_BLOCK(sb));
if (sb->s_magic != EXT2_SUPER_MAGIC)
goto cantfind_ext2;
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 813d589..b088686 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -1294,8 +1294,6 @@ #endif
sb->s_flags = s_flags; /* Restore MS_RDONLY status */
}
-#define log2(n) ffz(~(n))
-
/*
* Maximal file size. There is a direct, and {,double-,triple-}indirect
* block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
@@ -1543,8 +1541,8 @@ static int ext3_fill_super (struct super
sbi->s_desc_per_block = blocksize / sizeof(struct ext3_group_desc);
sbi->s_sbh = bh;
sbi->s_mount_state = le16_to_cpu(es->s_state);
- sbi->s_addr_per_block_bits = log2(EXT3_ADDR_PER_BLOCK(sb));
- sbi->s_desc_per_block_bits = log2(EXT3_DESC_PER_BLOCK(sb));
+ sbi->s_addr_per_block_bits = ilog2(EXT3_ADDR_PER_BLOCK(sb));
+ sbi->s_desc_per_block_bits = ilog2(EXT3_DESC_PER_BLOCK(sb));
for (i=0; i < 4; i++)
sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
sbi->s_def_hash_version = es->s_def_hash_version;
diff --git a/include/asm-frv/bitops.h b/include/asm-frv/bitops.h
index 1f70d47..f8560ed 100644
--- a/include/asm-frv/bitops.h
+++ b/include/asm-frv/bitops.h
@@ -256,6 +256,50 @@ int __ffs(unsigned long x)
return 31 - bit;
}
+/*
+ * special slimline version of fls() for calculating ilog2_u32()
+ * - note: no protection against n == 0
+ */
+#define ARCH_HAS_ILOG2_U32
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+ int bit;
+ asm("scan %1,gr0,%0" : "=r"(bit) : "r"(n));
+ return 31 - bit;
+}
+
+/*
+ * special slimline version of fls64() for calculating ilog2_u64()
+ * - note: no protection against n == 0
+ */
+#define ARCH_HAS_ILOG2_U64
+static inline __attribute__((const))
+int __ilog2_u64(u64 n)
+{
+ union {
+ u64 ll;
+ struct { u32 h, l; };
+ } _;
+ int bit, x, y;
+
+ _.ll = n;
+
+ asm(" subcc %3,gr0,gr0,icc0 \n"
+ " ckeq icc0,cc4 \n"
+ " cscan.p %3,gr0,%0 ,cc4,0 \n"
+ " setlos #63,%1 \n"
+ " cscan.p %4,gr0,%0 ,cc4,1 \n"
+ " setlos #31,%2 \n"
+ " csub.p %1,%0,%0 ,cc4,0 \n"
+ " csub %2,%0,%0 ,cc4,1 \n"
+ : "=&r"(bit), "=r"(x), "=r"(y)
+ : "0r"(_.h), "r"(_.l)
+ : "icc0", "cc4"
+ );
+ return bit;
+}
+
#include <asm-generic/bitops/sched.h>
#include <asm-generic/bitops/hweight.h>
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 851aa1b..e8c6c66 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -13,6 +13,7 @@ #include <linux/stddef.h>
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/bitops.h>
+#include <linux/log2.h>
#include <asm/byteorder.h>
#include <asm/bug.h>
@@ -154,14 +155,6 @@ #endif
unsigned long int_sqrt(unsigned long);
-static inline int __attribute_pure__ long_log2(unsigned long x)
-{
- int r = 0;
- for (x >>= 1; x > 0; x >>= 1)
- r++;
- return r;
-}
-
static inline unsigned long
__attribute_const__ roundup_pow_of_two(unsigned long x)
{
diff --git a/include/linux/log2.h b/include/linux/log2.h
new file mode 100644
index 0000000..6ce81b7
--- /dev/null
+++ b/include/linux/log2.h
@@ -0,0 +1,188 @@
+/* Integer base 2 logarithm calculation
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@...hat.com)
+ *
+ * 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 _LINUX_LOG2_H
+#define _LINUX_LOG2_H
+
+#include <linux/types.h>
+#include <linux/bitops.h>
+
+/*
+ * deal with unrepresentable constant logarithms
+ */
+extern __attribute__((const, noreturn))
+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()
+ */
+#ifndef ARCH_HAS_ILOG2_U32
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+ return fls(n) - 1;
+}
+#endif
+
+#ifndef ARCH_HAS_ILOG2_U64
+static inline __attribute__((const))
+int __ilog2_u64(u64 n)
+{
+ return fls64(n) - 1;
+}
+#endif
+
+/**
+ * ilog2_u32 - log of base 2 of 32-bit unsigned value
+ * @n - parameter
+ *
+ * constant-capable 32-bit log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ */
+#define ilog2_u32(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ n < 1 ? ____ilog2_NaN() : \
+ 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() \
+ ) : \
+ __ilog2_u32(n) \
+ )
+
+/**
+ * ilog2_u64 - log of base 2 of 64-bit unsigned value
+ * @n - parameter
+ *
+ * constant-capable 64-bit log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ */
+#define ilog2_u64(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() \
+ ) : \
+ __ilog2_u64(n) \
+ )
+
+/**
+ * ilog2 - log of base 2 of unsigned long value
+ * @n - parameter
+ *
+ * constant-capable unsigned long log of base 2 calculation
+ * - this can be used to initialise global variables from constant data
+ */
+#if BITS_PER_LONG == 32
+#define ilog2(n) ilog2_u32(n)
+#else
+#define ilog2(n) ilog2_u64(n)
+#endif
+
+#endif /* _LINUX_LOG2_H */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 54a4f53..2ccb960 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2420,7 +2420,7 @@ void *__init alloc_large_system_hash(con
if (numentries > max)
numentries = max;
- log2qty = long_log2(numentries);
+ log2qty = ilog2(numentries);
do {
size = bucketsize << log2qty;
@@ -2442,7 +2442,7 @@ void *__init alloc_large_system_hash(con
printk("%s hash table entries: %d (order: %d, %lu bytes)\n",
tablename,
(1U << log2qty),
- long_log2(size) - PAGE_SHIFT,
+ ilog2(size) - PAGE_SHIFT,
size);
if (_hash_shift)
-
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