[PATCH 1/4] LOG2: Implement a general integer log2 facility in the kernel [try #4]

David Howells
2006-10-06T13:35:04Z

From: David Howells <dhowells@redhat.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@redhat.com>
---

arch/alpha/Kconfig | 8 ++
arch/arm/Kconfig | 8 ++
arch/arm26/Kconfig | 8 ++
arch/avr32/Kconfig | 8 ++
arch/cris/Kconfig | 8 ++
arch/frv/Kconfig | 8 ++
arch/h8300/Kconfig | 8 ++
arch/i386/Kconfig.cpu | 8 ++
arch/ia64/Kconfig | 8 ++
arch/m32r/Kconfig | 8 ++
arch/m68k/Kconfig | 8 ++
arch/m68knommu/Kconfig | 8 ++
arch/mips/Kconfig | 8 ++
arch/parisc/Kconfig | 8 ++
arch/powerpc/Kconfig | 8 ++
arch/ppc/Kconfig | 8 ++
arch/s390/Kconfig | 8 ++
arch/sh/Kconfig | 8 ++
arch/sh64/Kconfig | 8 ++
arch/sparc/Kconfig | 8 ++
arch/sparc64/Kconfig | 8 ++
arch/v850/Kconfig | 8 ++
arch/x86_64/Kconfig | 8 ++
arch/xtensa/Kconfig | 8 ++
drivers/infiniband/hw/mthca/mthca_provider.c | 4 -
drivers/infiniband/hw/mthca/mthca_qp.c | 4 -
drivers/infiniband/hw/mthca/mthca_srq.c | 4 -
drivers/infiniband/ulp/iser/iser_memory.c | 4 -
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 | 131 ++++++++++++++++++++++++++
mm/page_alloc.c | 4 -
34 files changed, 382 insertions(+), 26 deletions(-)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 7e55ea6..84caf50 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -25,6 +25,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index adb05de..0c3dab6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -74,6 +74,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/arm26/Kconfig b/arch/arm26/Kconfig
index c14fe91..74eba8b 100644
--- a/arch/arm26/Kconfig
+++ b/arch/arm26/Kconfig
@@ -41,6 +41,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/avr32/Kconfig b/arch/avr32/Kconfig
index 5f1694e..bb059a4 100644
--- a/arch/avr32/Kconfig
+++ b/arch/avr32/Kconfig
@@ -45,6 +45,14 @@ config GENERIC_TIME
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_BUST_SPINLOCK
bool

diff --git a/arch/cris/Kconfig b/arch/cris/Kconfig
index 6a1238a..3474309 100644
--- a/arch/cris/Kconfig
+++ b/arch/cris/Kconfig
@@ -16,6 +16,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/frv/Kconfig b/arch/frv/Kconfig
index cf1c446..7561d7b 100644
--- a/arch/frv/Kconfig
+++ b/arch/frv/Kconfig
@@ -41,6 +41,14 @@ config TIME_LOW_RES
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default y
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default y
+
mainmenu "Fujitsu FR-V Kernel Configuration"

source "init/Kconfig"
diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index cabf0bf..34a84bc 100644
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -29,6 +29,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/i386/Kconfig.cpu b/arch/i386/Kconfig.cpu
index 21c9a4e..99fa842 100644
--- a/arch/i386/Kconfig.cpu
+++ b/arch/i386/Kconfig.cpu
@@ -240,6 +240,14 @@ config RWSEM_XCHGADD_ALGORITHM
depends on !M386
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_CALIBRATE_DELAY
bool
default y
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 70f7eb9..ac23182 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -34,6 +34,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/m32r/Kconfig b/arch/m32r/Kconfig
index 41fd490..f383dab 100644
--- a/arch/m32r/Kconfig
+++ b/arch/m32r/Kconfig
@@ -214,6 +214,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 805b81f..0953145 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -17,6 +17,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/m68knommu/Kconfig b/arch/m68knommu/Kconfig
index 6d920d4..0e07597 100644
--- a/arch/m68knommu/Kconfig
+++ b/arch/m68knommu/Kconfig
@@ -25,6 +25,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 8a49884..8f10fe2 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -789,6 +789,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index d210123..0f9ff61 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -25,6 +25,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_FIND_NEXT_BIT
bool
default y
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 8b69104..1cf67b7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -41,6 +41,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/ppc/Kconfig b/arch/ppc/Kconfig
index 077711e..55abcc9 100644
--- a/arch/ppc/Kconfig
+++ b/arch/ppc/Kconfig
@@ -19,6 +19,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 51c2dfe..a3f9550 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -22,6 +22,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index f6a0c44..eaea396 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -48,6 +48,14 @@ config GENERIC_IOMAP
config ARCH_MAY_HAVE_PC_FDC
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
source "init/Kconfig"

menu "System type"
diff --git a/arch/sh64/Kconfig b/arch/sh64/Kconfig
index 58c678e..03778a1 100644
--- a/arch/sh64/Kconfig
+++ b/arch/sh64/Kconfig
@@ -36,6 +36,14 @@ config GENERIC_CALIBRATE_DELAY
config RWSEM_XCHGADD_ALGORITHM
bool

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config GENERIC_ISA_DMA
bool

diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 9431e96..44b79c2 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -166,6 +166,14 @@ config ARCH_MAY_HAVE_PC_FDC
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config SUN_PM
bool
default y
diff --git a/arch/sparc64/Kconfig b/arch/sparc64/Kconfig
index b627f8d..d391d11 100644
--- a/arch/sparc64/Kconfig
+++ b/arch/sparc64/Kconfig
@@ -34,6 +34,14 @@ config ARCH_MAY_HAVE_PC_FDC
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
config AUDIT_ARCH
bool
default y
diff --git a/arch/v850/Kconfig b/arch/v850/Kconfig
index 37ec644..bcf8258 100644
--- a/arch/v850/Kconfig
+++ b/arch/v850/Kconfig
@@ -38,6 +38,14 @@ config TIME_LOW_RES
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
# Turn off some random 386 crap that can affect device config
config ISA
bool
diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig
index 010d226..c007ab2 100644
--- a/arch/x86_64/Kconfig
+++ b/arch/x86_64/Kconfig
@@ -96,6 +96,14 @@ config AUDIT_ARCH
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
source "init/Kconfig"

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index c1e69a1..9eccfbd 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -34,6 +34,14 @@ config GENERIC_HARDIRQS
bool
default y

+config ARCH_HAS_ILOG2_U32
+ bool
+ default n
+
+config ARCH_HAS_ILOG2_U64
+ bool
+ default n
+
source "init/Kconfig"

menu "Processor type and features"
diff --git a/drivers/infiniband/hw/mthca/mthca_provider.c b/drivers/infiniband/hw/mthca/mthca_provider.c
index 981fe2e..20c0fc1 100644
--- a/drivers/infiniband/hw/mthca/mthca_provider.c
+++ b/drivers/infiniband/hw/mthca/mthca_provider.c
@@ -124,7 +124,7 @@ static int mthca_query_device(struct ib_
props->max_map_per_fmr = 255;
else
props->max_map_per_fmr =
- (1 << (32 - long_log2(mdev->limits.num_mpts))) - 1;
+ (1 << (32 - ilog2(mdev->limits.num_mpts))) - 1;

err = 0;
out:
@@ -814,7 +814,7 @@ static int mthca_resize_cq(struct ib_cq
lkey = ucmd.lkey;
}

- ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, long_log2(entries), &status);
+ ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, ilog2(entries), &status);
if (status)
ret = -EINVAL;

diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index 5e5c58b..1bf0856 100644
--- a/drivers/infiniband/hw/mthca/mthca_qp.c
+++ b/drivers/infiniband/hw/mthca/mthca_qp.c
@@ -635,11 +635,11 @@ int mthca_modify_qp(struct ib_qp *ibqp,

if (mthca_is_memfree(dev)) {
if (qp->rq.max)
- qp_context->rq_size_stride = long_log2(qp->rq.max) << 3;
+ qp_context->rq_size_stride = ilog2(qp->rq.max) << 3;
qp_context->rq_size_stride |= qp->rq.wqe_shift - 4;

if (qp->sq.max)
- qp_context->sq_size_stride = long_log2(qp->sq.max) << 3;
+ qp_context->sq_size_stride = ilog2(qp->sq.max) << 3;
qp_context->sq_size_stride |= qp->sq.wqe_shift - 4;
}

diff --git a/drivers/infiniband/hw/mthca/mthca_srq.c b/drivers/infiniband/hw/mthca/mthca_srq.c
index 0f316c8..2af1b8e 100644
--- a/drivers/infiniband/hw/mthca/mthca_srq.c
+++ b/drivers/infiniband/hw/mthca/mthca_srq.c
@@ -118,7 +118,7 @@ static void mthca_arbel_init_srq_context

memset(context, 0, sizeof *context);

- logsize = long_log2(srq->max) + srq->wqe_shift;
+ logsize = ilog2(srq->max) + srq->wqe_shift;
context->state_logsize_srqn = cpu_to_be32(logsize << 24 | srq->srqn);
context->lkey = cpu_to_be32(srq->mr.ibmr.lkey);
context->db_index = cpu_to_be32(srq->db_index);
@@ -209,7 +209,7 @@ int mthca_alloc_srq(struct mthca_dev *de
if (!mthca_is_memfree(dev) && (ds > dev->limits.max_desc_sz))
return -EINVAL;

- srq->wqe_shift = long_log2(ds);
+ srq->wqe_shift = ilog2(ds);

srq->srqn = mthca_alloc(&dev->srq_table.alloc);
if (srq->srqn == -1)
diff --git a/drivers/infiniband/ulp/iser/iser_memory.c b/drivers/infiniband/ulp/iser/iser_memory.c
index 0606744..15de90e 100644
--- a/drivers/infiniband/ulp/iser/iser_memory.c
+++ b/drivers/infiniband/ulp/iser/iser_memory.c
@@ -113,7 +113,7 @@ int iser_start_rdma_unaligned_sg(struct

if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
mem = (void *)__get_free_pages(GFP_NOIO,
- long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
+ ilog2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
else
mem = kmalloc(cmd_data_len, GFP_NOIO);

@@ -210,7 +210,7 @@ void iser_finalize_rdma_unaligned_sg(str

if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
free_pages((unsigned long)mem_copy->copy_buf,
- long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
+ ilog2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
else
kfree(mem_copy->copy_buf);

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 513cd42..4f0bd87 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -593,8 +593,6 @@ 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.
@@ -828,9 +826,9 @@ 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 8bfd56e..b97119c 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -1341,8 +1341,6 @@ #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.
@@ -1589,8 +1587,8 @@ 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 80f39ca..473101a 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>

@@ -155,14 +156,6 @@ #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..3979c60
--- /dev/null
+++ b/include/linux/log2.h
@@ -0,0 +1,131 @@
+/* Integer base 2 logarithm calculation
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.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()
+ * - the arch is not required to handle n==0 if implementing the fallback
+ */
+#ifndef CONFIG_ARCH_HAS_ILOG2_U32
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+ return fls(n) - 1;
+}
+#endif
+
+#ifndef CONFIG_ARCH_HAS_ILOG2_U64
+static inline __attribute__((const))
+int __ilog2_u64(u64 n)
+{
+ return fls64(n) - 1;
+}
+#endif
+
+/**
+ * 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) \
+ )
+
+#endif /* _LINUX_LOG2_H */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a8c003e..bd30dff 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3091,7 +3091,7 @@ void *__init alloc_large_system_hash(con
if (numentries > max)
numentries = max;

- log2qty = long_log2(numentries);
+ log2qty = ilog2(numentries);

do {
size = bucketsize << log2qty;
@@ -3113,7 +3113,7 @@ 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)