Messages in this thread Patch in this message | | | From | David Howells <> | Subject | [PATCH 4/7] Implement a general integer log2 facility in the kernel [try #3] | Date | Wed, 13 Sep 2006 19:35:29 +0100 |
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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> ---
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 | 188 ++++++++++++++++++++++++++ mm/page_alloc.c | 4 - 10 files changed, 247 insertions(+), 26 deletions(-)
diff --git a/drivers/infiniband/hw/mthca/mthca_provider.c b/drivers/infiniband/hw/mthca/mthca_provider.c index 265b1d1..413dd6d 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 2e8f6f3..bace21e 100644 --- a/drivers/infiniband/hw/mthca/mthca_qp.c +++ b/drivers/infiniband/hw/mthca/mthca_qp.c @@ -632,11 +632,11 @@ 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 b60a9d7..69d842b 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 31950a5..13aeeba 100644 --- a/drivers/infiniband/ulp/iser/iser_memory.c +++ b/drivers/infiniband/ulp/iser/iser_memory.c @@ -112,7 +112,7 @@ 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); @@ -209,7 +209,7 @@ 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 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@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() + */ +#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) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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