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Denys Vlasenko 133fd9f5cd vsprintf: further optimize decimal conversion 
Previous code was using optimizations which were developed to work well
even on narrow-word CPUs (by today's standards).  But Linux runs only on
32-bit and wider CPUs.  We can use that.

First: using 32x32->64 multiply and trivial 32-bit shift, we can correctly
divide by 10 much larger numbers, and thus we can print groups of 9 digits
instead of groups of 5 digits.

Next: there are two algorithms to print larger numbers.  One is generic:
divide by 1000000000 and repeatedly print groups of (up to) 9 digits.
It's conceptually simple, but requires an (unsigned long long) /
1000000000 division.

Second algorithm splits 64-bit unsigned long long into 16-bit chunks,
manipulates them cleverly and generates groups of 4 decimal digits.  It so
happens that it does NOT require long long division.

If long is > 32 bits, division of 64-bit values is relatively easy, and we
will use the first algorithm.  If long long is > 64 bits (strange
architecture with VERY large long long), second algorithm can't be used,
and we again use the first one.

Else (if long is 32 bits and long long is 64 bits) we use second one.

And third: there is a simple optimization which takes fast path not only
for zero as was done before, but for all one-digit numbers.

In all tested cases new code is faster than old one, in many cases by 30%,
in few cases by more than 50% (for example, on x86-32, conversion of
12345678).  Code growth is ~0 in 32-bit case and ~130 bytes in 64-bit
case.

This patch is based upon an original from Michal Nazarewicz.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Douglas W Jones <jones@cs.uiowa.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2012-05-31 17:49:27 -07:00
..
lzo
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mpi mpi: Avoid using freed pointer in mpi_lshift_limbs() 2012-04-18 12:14:28 +10:00
raid6 lib/raid6: cleanup gen_syndrome function selection 2012-05-22 13:54:24 +10:00
reed_solomon
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xz
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zlib_deflate
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zlib_inflate
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.gitignore
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Kconfig Merge branch 'generic-string-functions' 2012-05-26 16:57:16 -07:00
Kconfig.debug Merge branches 'x86-asm-for-linus', 'x86-cleanups-for-linus', 'x86-cpu-for-linus', 'x86-debug-for-linus' and 'x86-microcode-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-05-23 10:09:50 -07:00
Kconfig.kgdb
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Kconfig.kmemcheck
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Makefile Merge branch 'generic-string-functions' 2012-05-26 16:57:16 -07:00
argv_split.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
atomic64.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
atomic64_test.c bug.h: add include of it to various implicit C users 2012-02-29 17:15:08 -05:00
audit.c
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average.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
bcd.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
bch.c
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bitmap.c lib/bitmap.c: fix documentation for scnprintf() functions 2012-05-29 16:22:32 -07:00
bitrev.c
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bsearch.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
btree.c btree: export btree_get_prev() so modules can use btree_for_each 2012-01-10 16:30:49 -08:00
bug.c bugs, x86: Fix printk levels for panic, softlockups and stack dumps 2012-01-26 21:28:45 +01:00
bust_spinlocks.c
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check_signature.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
checksum.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
clz_tab.c lib: Fix multiple definitions of clz_tab 2012-02-02 10:34:23 +11:00
cmdline.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
cordic.c Docs: wording: functions -> algorithm 2011-10-29 21:20:22 +02:00
cpu-notifier-error-inject.c
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cpu_rmap.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
cpumask.c lib/cpumask.c: remove __any_online_cpu() 2012-03-28 17:14:35 -07:00
crc-ccitt.c
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crc-itu-t.c
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crc-t10dif.c
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crc7.c
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crc8.c
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crc16.c
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crc32.c crc32: add self-test code for crc32c 2012-03-23 16:58:38 -07:00
crc32defs.h crc32: select an algorithm via Kconfig 2012-03-23 16:58:38 -07:00
ctype.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
debug_locks.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
debugobjects.c debugobjects: Fill_pool() returns void now 2012-04-18 13:38:48 +02:00
dec_and_lock.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
decompress.c
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decompress_bunzip2.c decompress_bunzip2: remove invalid vi modeline 2011-12-06 10:00:05 +01:00
decompress_inflate.c
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decompress_unlzma.c treewide: Fix comment and string typo 'bufer' 2011-12-06 09:53:40 +01:00
decompress_unlzo.c unlzo: fix input buffer free 2012-01-12 20:13:13 -08:00
decompress_unxz.c
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devres.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
digsig.c lib/digsig: checks for NULL return value 2012-02-02 00:24:04 +11:00
div64.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
dma-debug.c Remove useless get_driver()/put_driver() calls 2012-01-24 16:00:35 -08:00
dump_stack.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
dynamic_debug.c Revert "dynamic_debug: remove unneeded includes" 2012-05-07 16:47:32 -07:00
dynamic_queue_limits.c dql: Fix undefined jiffies 2012-03-11 19:59:43 -07:00
extable.c
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fault-inject.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
find_last_bit.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
find_next_bit.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
flex_array.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
gcd.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
gen_crc32table.c crc32: bolt on crc32c 2012-03-23 16:58:38 -07:00
genalloc.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
halfmd4.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
hexdump.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
hweight.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
idr.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
inflate.c
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int_sqrt.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
iomap.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
iomap_copy.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
iommu-helper.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
ioremap.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
irq_regs.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
is_single_threaded.c
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jedec_ddr_data.c ddr: add LPDDR2 data from JESD209-2 2012-05-02 00:04:06 -07:00
kasprintf.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
klist.c Revert "driver core: check start node in klist_iter_init_node" 2012-04-19 19:17:30 -07:00
kobject.c kobject: fix the uncorrect comment 2012-05-07 16:51:19 -07:00
kobject_uevent.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
kstrtox.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
kstrtox.h lib/kstrtox: common code between kstrto*() and simple_strto*() functions 2011-10-31 17:30:56 -07:00
lcm.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
libcrc32c.c
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list_debug.c list_debug: WARN for adding something already in the list 2012-05-29 16:22:32 -07:00
list_sort.c
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llist.c Disintegrate and delete asm/system.h 2012-03-28 15:58:21 -07:00
locking-selftest-hardirq.h
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locking-selftest-mutex.h
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locking-selftest-rlock-hardirq.h
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locking-selftest-rlock-softirq.h
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locking-selftest-rlock.h
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locking-selftest-rsem.h
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locking-selftest-softirq.h
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locking-selftest-spin-hardirq.h
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locking-selftest-spin-softirq.h
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locking-selftest-spin.h
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locking-selftest-wlock-hardirq.h
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locking-selftest-wlock-softirq.h
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locking-selftest-wlock.h
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locking-selftest-wsem.h
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locking-selftest.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
lru_cache.c
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md5.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
nlattr.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
parser.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
pci_iomap.c lib: add NO_GENERIC_PCI_IOPORT_MAP 2012-01-31 23:19:47 +02:00
percpu_counter.c lib/percpu_counter.c: enclose hotplug only variables in hotplug ifdef 2011-10-31 17:30:56 -07:00
plist.c bug.h: add include of it to various implicit C users 2012-02-29 17:15:08 -05:00
prio_heap.c
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prio_tree.c prio_tree: introduce prio_set_parent() 2012-03-23 16:58:36 -07:00
proportions.c
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radix-tree.c radix-tree: fix preload vector size 2012-05-29 16:22:33 -07:00
random32.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
ratelimit.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
rational.c lib: Change mail address of Oskar Schirmer 2012-05-17 15:18:37 +02:00
rbtree.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
reciprocal_div.c sch_red: Adaptative RED AQM 2011-12-08 19:52:43 -05:00
rwsem-spinlock.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
rwsem.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
scatterlist.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
sha1.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
show_mem.c
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smp_processor_id.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
sort.c
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spinlock_debug.c spinlock_debug: print kallsyms name for lock 2012-05-29 16:22:33 -07:00
stmp_device.c lib: add support for stmp-style devices 2012-04-20 23:27:08 +02:00
string.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
string_helpers.c lib/string_helpers.c: make arrays static 2012-05-29 16:22:32 -07:00
strncpy_from_user.c word-at-a-time: make the interfaces truly generic 2012-05-26 11:33:40 -07:00
strnlen_user.c lib: Fix generic strnlen_user for 32-bit big-endian machines 2012-05-27 20:59:46 -07:00
swiotlb.c swiotlb: print physical addresses consistently with other parts of kernel 2012-05-29 16:22:21 -07:00
syscall.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
test-kstrtox.c lib/test-kstrtox.c: mark const init data with __initconst instead of __initdata 2012-05-29 16:22:32 -07:00
textsearch.c
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timerqueue.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
ts_bm.c
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ts_fsm.c
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ts_kmp.c
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uuid.c lib: reduce the use of module.h wherever possible 2012-03-07 15:04:04 -05:00
vsprintf.c vsprintf: further optimize decimal conversion 2012-05-31 17:49:27 -07:00