avoid overflows in kernel/time.c

When the conversion factor between jiffies and milli- or microseconds is
not a single multiply or divide, as for the case of HZ == 300, we currently
do a multiply followed by a divide.  The intervening result, however, is
subject to overflows, especially since the fraction is not simplified (for
HZ == 300, we multiply by 300 and divide by 1000).

This is exposed to the user when passing a large timeout to poll(), for
example.

This patch replaces the multiply-divide with a reciprocal multiplication on
32-bit platforms.  When the input is an unsigned long, there is no portable
way to do this on 64-bit platforms there is no portable way to do this
since it requires a 128-bit intermediate result (which gcc does support on
64-bit platforms but may generate libgcc calls, e.g.  on 64-bit s390), but
since the output is a 32-bit integer in the cases affected, just simplify
the multiply-divide (*3/10 instead of *300/1000).

The reciprocal multiply used can have off-by-one errors in the upper half
of the valid output range.  This could be avoided at the expense of having
to deal with a potential 65-bit intermediate result.  Since the intent is
to avoid overflow problems and most of the other time conversions are only
semiexact, the off-by-one errors were considered an acceptable tradeoff.

At Ralf Baechle's suggestion, this version uses a Perl script to compute
the necessary constants.  We already have dependencies on Perl for kernel
compiles.  This does, however, require the Perl module Math::BigInt, which
is included in the standard Perl distribution starting with version 5.8.0.
In order to support older versions of Perl, include a table of canned
constants in the script itself, and structure the script so that
Math::BigInt isn't required if pulling values from said table.

Running the script requires that the HZ value is available from the
Makefile.  Thus, this patch also adds the Kconfig variable CONFIG_HZ to the
architectures which didn't already have it (alpha, cris, frv, h8300, m32r,
m68k, m68knommu, sparc, v850, and xtensa.) It does *not* touch the sh or
sh64 architectures, since Paul Mundt has dealt with those separately in the
sh tree.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
Cc: Sam Ravnborg <sam@ravnborg.org>,
Cc: Paul Mundt <lethal@linux-sh.org>,
Cc: Richard Henderson <rth@twiddle.net>,
Cc: Michael Starvik <starvik@axis.com>,
Cc: David Howells <dhowells@redhat.com>,
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>,
Cc: Hirokazu Takata <takata@linux-m32r.org>,
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Cc: Roman Zippel <zippel@linux-m68k.org>,
Cc: William L. Irwin <sparclinux@vger.kernel.org>,
Cc: Chris Zankel <chris@zankel.net>,
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
H. Peter Anvin 2008-02-08 04:21:26 -08:00 committed by Linus Torvalds
parent 7ef3d2fd17
commit bdc807871d
29 changed files with 486 additions and 68 deletions

View File

@ -615,6 +615,11 @@ config VERBOSE_MCHECK_ON
Take the default (1) unless you want more control or more info.
config HZ
int
default 1200 if ALPHA_RAWHIDE
default 1024
source "drivers/pci/Kconfig"
source "drivers/eisa/Kconfig"

View File

@ -55,6 +55,10 @@ config CRIS
bool
default y
config HZ
int
default 100
source "init/Kconfig"
menu "General setup"

View File

@ -57,6 +57,10 @@ config ARCH_HAS_ILOG2_U64
bool
default y
config HZ
int
default 1000
mainmenu "Fujitsu FR-V Kernel Configuration"
source "init/Kconfig"

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@ -82,6 +82,10 @@ config PCI
bool
default n
config HZ
int
default 100
source "init/Kconfig"
source "arch/h8300/Kconfig.cpu"

View File

@ -38,6 +38,10 @@ config NO_DMA
config ARCH_SUPPORTS_AOUT
def_bool y
config HZ
int
default 100
source "init/Kconfig"

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@ -55,6 +55,10 @@ config NO_DMA
config ARCH_SUPPORTS_AOUT
def_bool y
config HZ
int
default 100
mainmenu "Linux/68k Kernel Configuration"
source "init/Kconfig"

View File

@ -525,6 +525,11 @@ config 4KSTACKS
running more threads on a system and also reduces the pressure
on the VM subsystem for higher order allocations.
config HZ
int
default 1000 if CLEOPATRA
default 100
comment "RAM configuration"
config RAMBASE

View File

@ -30,6 +30,10 @@ config OF
config ARCH_SUPPORTS_AOUT
def_bool y
config HZ
int
default 100
source "init/Kconfig"
menu "General machine setup"

View File

@ -215,6 +215,13 @@ menu "Processor type and features"
bool
default !V850E_CACHE && !V850E2_CACHE
# HZ depends on the platform
config HZ
int
default 24 if V850E_SIM || V850E2_SIM85E2
default 122 if V850E2_FPGA85E2C
default 100
#### Misc config
config ROM_KERNEL

View File

@ -49,6 +49,10 @@ config ARCH_HAS_ILOG2_U64
config NO_IOPORT
def_bool y
config HZ
int
default 100
source "init/Kconfig"
menu "Processor type and features"

View File

@ -5,15 +5,7 @@
hardware ignores reprogramming. We also need userland buy-in to the
change in HZ, since this is visible in the wait4 resources etc. */
#ifndef HZ
# ifndef CONFIG_ALPHA_RAWHIDE
# define HZ 1024
# else
# define HZ 1200
# endif
#endif
#define HZ CONFIG_HZ
#define USER_HZ HZ
#define EXEC_PAGESIZE 8192

View File

@ -3,7 +3,7 @@
/* Currently we assume that HZ=100 is good for CRIS. */
#ifdef __KERNEL__
# define HZ 100 /* Internal kernel timer frequency */
# define HZ CONFIG_HZ /* Internal kernel timer frequency */
# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
# define CLOCKS_PER_SEC (USER_HZ) /* like times() */
#endif

View File

@ -2,7 +2,7 @@
#define _ASM_PARAM_H
#ifdef __KERNEL__
#define HZ 1000 /* Internal kernel timer frequency */
#define HZ CONFIG_HZ /* Internal kernel timer frequency */
#define USER_HZ 100 /* .. some user interfaces are in "ticks" */
#define CLOCKS_PER_SEC (USER_HZ) /* like times() */
#endif

View File

@ -3,7 +3,7 @@
#ifndef HZ
#define HZ 100
#define HZ CONFIG_HZ
#endif
#ifdef __KERNEL__

View File

@ -2,7 +2,7 @@
#define _ASM_M32R_PARAM_H
#ifdef __KERNEL__
# define HZ 100 /* Internal kernel timer frequency */
# define HZ CONFIG_HZ /* Internal kernel timer frequency */
# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
# define CLOCKS_PER_SEC (USER_HZ) /* like times() */
#endif

View File

@ -2,7 +2,7 @@
#define _M68K_PARAM_H
#ifdef __KERNEL__
# define HZ 100 /* Internal kernel timer frequency */
# define HZ CONFIG_HZ /* Internal kernel timer frequency */
# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
# define CLOCKS_PER_SEC (USER_HZ) /* like times() */
#endif

View File

@ -1,13 +1,7 @@
#ifndef _M68KNOMMU_PARAM_H
#define _M68KNOMMU_PARAM_H
#if defined(CONFIG_CLEOPATRA)
#define HZ 1000
#endif
#ifndef HZ
#define HZ 100
#endif
#define HZ CONFIG_HZ
#ifdef __KERNEL__
#define USER_HZ HZ

View File

@ -3,7 +3,7 @@
#define _ASMSPARC_PARAM_H
#ifdef __KERNEL__
# define HZ 100 /* Internal kernel timer frequency */
# define HZ CONFIG_HZ /* Internal kernel timer frequency */
# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
# define CLOCKS_PER_SEC (USER_HZ)
#endif

View File

@ -134,10 +134,4 @@ extern void anna_uart_pre_configure (unsigned chan,
#define V850E_TIMER_D_TMCD_CS_MIN 1 /* min 2^1 divider */
/* For <asm/param.h> */
#ifndef HZ
#define HZ 100
#endif
#endif /* __V850_ANNA_H__ */

View File

@ -149,10 +149,4 @@ extern void as85ep1_uart_pre_configure (unsigned chan,
#define V850E_TIMER_D_TMCD_CS_MIN 2 /* min 2^2 divider */
/* For <asm/param.h> */
#ifndef HZ
#define HZ 100
#endif
#endif /* __V850_AS85EP1_H__ */

View File

@ -79,10 +79,4 @@ extern char _r0_ram;
#endif
/* For <asm/param.h> */
#ifndef HZ
#define HZ 122 /* actually, 8.192ms ticks =~ 122.07 */
#endif
#endif /* __V850_FPGA85E2C_H__ */

View File

@ -23,8 +23,7 @@
#define MAXHOSTNAMELEN 64 /* max length of hostname */
#ifdef __KERNEL__
#include <asm/machdep.h> /* For HZ */
# define HZ CONFIG_HZ
# define USER_HZ 100
# define CLOCKS_PER_SEC USER_HZ
#endif

View File

@ -69,12 +69,6 @@
#endif /* CONFIG_RTE_MB_A_PCI */
/* For <asm/param.h> */
#ifndef HZ
#define HZ 100
#endif
#ifndef __ASSEMBLY__
extern void rte_cb_early_init (void);
extern void rte_cb_init_irqs (void);

View File

@ -40,11 +40,6 @@
#define R0_RAM_ADDR 0xFFFFF000
/* For <asm/param.h> */
#ifndef HZ
#define HZ 24 /* Minimum supported frequency. */
#endif
/* For <asm/irq.h> */
#define NUM_CPU_IRQS 6

View File

@ -66,10 +66,4 @@
#define R0_RAM_ADDR 0xFFFFE000
/* For <asm/param.h> */
#ifndef HZ
#define HZ 24 /* Minimum supported frequency. */
#endif
#endif /* __V850_SIM85E2_H__ */

View File

@ -12,7 +12,7 @@
#define _XTENSA_PARAM_H
#ifdef __KERNEL__
# define HZ 100 /* internal timer frequency */
# define HZ CONFIG_HZ /* internal timer frequency */
# define USER_HZ 100 /* for user interfaces in "ticks" */
# define CLOCKS_PER_SEC (USER_HZ) /* frequnzy at which times() counts */
#endif

View File

@ -91,3 +91,11 @@ quiet_cmd_ikconfiggz = IKCFG $@
targets += config_data.h
$(obj)/config_data.h: $(obj)/config_data.gz FORCE
$(call if_changed,ikconfiggz)
$(obj)/time.o: $(obj)/timeconst.h
quiet_cmd_timeconst = TIMEC $@
cmd_timeconst = $(PERL) $< $(CONFIG_HZ) > $@
targets += timeconst.h
$(obj)/timeconst.h: $(src)/timeconst.pl FORCE
$(call if_changed,timeconst)

View File

@ -39,6 +39,8 @@
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include "timeconst.h"
/*
* The timezone where the local system is located. Used as a default by some
* programs who obtain this value by using gettimeofday.
@ -93,7 +95,8 @@ asmlinkage long sys_stime(time_t __user *tptr)
#endif /* __ARCH_WANT_SYS_TIME */
asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __user *tz)
asmlinkage long sys_gettimeofday(struct timeval __user *tv,
struct timezone __user *tz)
{
if (likely(tv != NULL)) {
struct timeval ktv;
@ -118,7 +121,7 @@ asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __us
* hard to make the program warp the clock precisely n hours) or
* compile in the timezone information into the kernel. Bad, bad....
*
* - TYT, 1992-01-01
* - TYT, 1992-01-01
*
* The best thing to do is to keep the CMOS clock in universal time (UTC)
* as real UNIX machines always do it. This avoids all headaches about
@ -240,7 +243,11 @@ unsigned int inline jiffies_to_msecs(const unsigned long j)
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
#else
return (j * MSEC_PER_SEC) / HZ;
# if BITS_PER_LONG == 32
return ((u64)HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
# else
return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_msecs);
@ -252,7 +259,11 @@ unsigned int inline jiffies_to_usecs(const unsigned long j)
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
#else
return (j * USEC_PER_SEC) / HZ;
# if BITS_PER_LONG == 32
return ((u64)HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
# else
return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
# endif
#endif
}
EXPORT_SYMBOL(jiffies_to_usecs);
@ -352,7 +363,7 @@ EXPORT_SYMBOL(mktime);
* normalize to the timespec storage format
*
* Note: The tv_nsec part is always in the range of
* 0 <= tv_nsec < NSEC_PER_SEC
* 0 <= tv_nsec < NSEC_PER_SEC
* For negative values only the tv_sec field is negative !
*/
void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
@ -453,12 +464,13 @@ unsigned long msecs_to_jiffies(const unsigned int m)
/*
* Generic case - multiply, round and divide. But first
* check that if we are doing a net multiplication, that
* we wouldnt overflow:
* we wouldn't overflow:
*/
if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
return MAX_JIFFY_OFFSET;
return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;
return ((u64)MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
>> MSEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(msecs_to_jiffies);
@ -472,7 +484,8 @@ unsigned long usecs_to_jiffies(const unsigned int u)
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
return u * (HZ / USEC_PER_SEC);
#else
return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC;
return ((u64)USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
>> USEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(usecs_to_jiffies);

402
kernel/timeconst.pl Normal file
View File

@ -0,0 +1,402 @@
#!/usr/bin/perl
# -----------------------------------------------------------------------
#
# Copyright 2007 rPath, Inc. - All Rights Reserved
#
# This file is part of the Linux kernel, and is made available under
# the terms of the GNU General Public License version 2 or (at your
# option) any later version; incorporated herein by reference.
#
# -----------------------------------------------------------------------
#
#
# Usage: timeconst.pl HZ > timeconst.h
#
# Precomputed values for systems without Math::BigInt
# Generated by:
# timeconst.pl --can 24 32 48 64 100 122 128 200 250 256 300 512 1000 1024 1200
%canned_values = (
24 => [
'0xa6aaaaab','0x2aaaaaa',26,
'0xa6aaaaaaaaaaaaab','0x2aaaaaaaaaaaaaa',58,
125,3,
'0xc49ba5e4','0x1fbe76c8b4',37,
'0xc49ba5e353f7ceda','0x1fbe76c8b439581062',69,
3,125,
'0xa2c2aaab','0xaaaa',16,
'0xa2c2aaaaaaaaaaab','0xaaaaaaaaaaaa',48,
125000,3,
'0xc9539b89','0x7fffbce4217d',47,
'0xc9539b8887229e91','0x7fffbce4217d2849cb25',79,
3,125000,
], 32 => [
'0xfa000000','0x6000000',27,
'0xfa00000000000000','0x600000000000000',59,
125,4,
'0x83126e98','0xfdf3b645a',36,
'0x83126e978d4fdf3c','0xfdf3b645a1cac0831',68,
4,125,
'0xf4240000','0x0',17,
'0xf424000000000000','0x0',49,
31250,1,
'0x8637bd06','0x3fff79c842fa',46,
'0x8637bd05af6c69b6','0x3fff79c842fa5093964a',78,
1,31250,
], 48 => [
'0xa6aaaaab','0x6aaaaaa',27,
'0xa6aaaaaaaaaaaaab','0x6aaaaaaaaaaaaaa',59,
125,6,
'0xc49ba5e4','0xfdf3b645a',36,
'0xc49ba5e353f7ceda','0xfdf3b645a1cac0831',68,
6,125,
'0xa2c2aaab','0x15555',17,
'0xa2c2aaaaaaaaaaab','0x1555555555555',49,
62500,3,
'0xc9539b89','0x3fffbce4217d',46,
'0xc9539b8887229e91','0x3fffbce4217d2849cb25',78,
3,62500,
], 64 => [
'0xfa000000','0xe000000',28,
'0xfa00000000000000','0xe00000000000000',60,
125,8,
'0x83126e98','0x7ef9db22d',35,
'0x83126e978d4fdf3c','0x7ef9db22d0e560418',67,
8,125,
'0xf4240000','0x0',18,
'0xf424000000000000','0x0',50,
15625,1,
'0x8637bd06','0x1fff79c842fa',45,
'0x8637bd05af6c69b6','0x1fff79c842fa5093964a',77,
1,15625,
], 100 => [
'0xa0000000','0x0',28,
'0xa000000000000000','0x0',60,
10,1,
'0xcccccccd','0x733333333',35,
'0xcccccccccccccccd','0x73333333333333333',67,
1,10,
'0x9c400000','0x0',18,
'0x9c40000000000000','0x0',50,
10000,1,
'0xd1b71759','0x1fff2e48e8a7',45,
'0xd1b71758e219652c','0x1fff2e48e8a71de69ad4',77,
1,10000,
], 122 => [
'0x8325c53f','0xfbcda3a',28,
'0x8325c53ef368eb05','0xfbcda3ac10c9714',60,
500,61,
'0xf9db22d1','0x7fbe76c8b',35,
'0xf9db22d0e560418a','0x7fbe76c8b43958106',67,
61,500,
'0x8012e2a0','0x3ef36',18,
'0x8012e29f79b47583','0x3ef368eb04325',50,
500000,61,
'0xffda4053','0x1ffffbce4217',45,
'0xffda4052d666a983','0x1ffffbce4217d2849cb2',77,
61,500000,
], 128 => [
'0xfa000000','0x1e000000',29,
'0xfa00000000000000','0x1e00000000000000',61,
125,16,
'0x83126e98','0x3f7ced916',34,
'0x83126e978d4fdf3c','0x3f7ced916872b020c',66,
16,125,
'0xf4240000','0x40000',19,
'0xf424000000000000','0x4000000000000',51,
15625,2,
'0x8637bd06','0xfffbce4217d',44,
'0x8637bd05af6c69b6','0xfffbce4217d2849cb25',76,
2,15625,
], 200 => [
'0xa0000000','0x0',29,
'0xa000000000000000','0x0',61,
5,1,
'0xcccccccd','0x333333333',34,
'0xcccccccccccccccd','0x33333333333333333',66,
1,5,
'0x9c400000','0x0',19,
'0x9c40000000000000','0x0',51,
5000,1,
'0xd1b71759','0xfff2e48e8a7',44,
'0xd1b71758e219652c','0xfff2e48e8a71de69ad4',76,
1,5000,
], 250 => [
'0x80000000','0x0',29,
'0x8000000000000000','0x0',61,
4,1,
'0x80000000','0x180000000',33,
'0x8000000000000000','0x18000000000000000',65,
1,4,
'0xfa000000','0x0',20,
'0xfa00000000000000','0x0',52,
4000,1,
'0x83126e98','0x7ff7ced9168',43,
'0x83126e978d4fdf3c','0x7ff7ced916872b020c4',75,
1,4000,
], 256 => [
'0xfa000000','0x3e000000',30,
'0xfa00000000000000','0x3e00000000000000',62,
125,32,
'0x83126e98','0x1fbe76c8b',33,
'0x83126e978d4fdf3c','0x1fbe76c8b43958106',65,
32,125,
'0xf4240000','0xc0000',20,
'0xf424000000000000','0xc000000000000',52,
15625,4,
'0x8637bd06','0x7ffde7210be',43,
'0x8637bd05af6c69b6','0x7ffde7210be9424e592',75,
4,15625,
], 300 => [
'0xd5555556','0x2aaaaaaa',30,
'0xd555555555555556','0x2aaaaaaaaaaaaaaa',62,
10,3,
'0x9999999a','0x1cccccccc',33,
'0x999999999999999a','0x1cccccccccccccccc',65,
3,10,
'0xd0555556','0xaaaaa',20,
'0xd055555555555556','0xaaaaaaaaaaaaa',52,
10000,3,
'0x9d495183','0x7ffcb923a29',43,
'0x9d495182a9930be1','0x7ffcb923a29c779a6b5',75,
3,10000,
], 512 => [
'0xfa000000','0x7e000000',31,
'0xfa00000000000000','0x7e00000000000000',63,
125,64,
'0x83126e98','0xfdf3b645',32,
'0x83126e978d4fdf3c','0xfdf3b645a1cac083',64,
64,125,
'0xf4240000','0x1c0000',21,
'0xf424000000000000','0x1c000000000000',53,
15625,8,
'0x8637bd06','0x3ffef39085f',42,
'0x8637bd05af6c69b6','0x3ffef39085f4a1272c9',74,
8,15625,
], 1000 => [
'0x80000000','0x0',31,
'0x8000000000000000','0x0',63,
1,1,
'0x80000000','0x0',31,
'0x8000000000000000','0x0',63,
1,1,
'0xfa000000','0x0',22,
'0xfa00000000000000','0x0',54,
1000,1,
'0x83126e98','0x1ff7ced9168',41,
'0x83126e978d4fdf3c','0x1ff7ced916872b020c4',73,
1,1000,
], 1024 => [
'0xfa000000','0xfe000000',32,
'0xfa00000000000000','0xfe00000000000000',64,
125,128,
'0x83126e98','0x7ef9db22',31,
'0x83126e978d4fdf3c','0x7ef9db22d0e56041',63,
128,125,
'0xf4240000','0x3c0000',22,
'0xf424000000000000','0x3c000000000000',54,
15625,16,
'0x8637bd06','0x1fff79c842f',41,
'0x8637bd05af6c69b6','0x1fff79c842fa5093964',73,
16,15625,
], 1200 => [
'0xd5555556','0xd5555555',32,
'0xd555555555555556','0xd555555555555555',64,
5,6,
'0x9999999a','0x66666666',31,
'0x999999999999999a','0x6666666666666666',63,
6,5,
'0xd0555556','0x2aaaaa',22,
'0xd055555555555556','0x2aaaaaaaaaaaaa',54,
2500,3,
'0x9d495183','0x1ffcb923a29',41,
'0x9d495182a9930be1','0x1ffcb923a29c779a6b5',73,
3,2500,
]
);
$has_bigint = eval 'use Math::BigInt qw(bgcd); 1;';
sub bint($)
{
my($x) = @_;
return Math::BigInt->new($x);
}
#
# Constants for division by reciprocal multiplication.
# (bits, numerator, denominator)
#
sub fmul($$$)
{
my ($b,$n,$d) = @_;
$n = bint($n);
$d = bint($d);
return scalar (($n << $b)+$d-bint(1))/$d;
}
sub fadj($$$)
{
my($b,$n,$d) = @_;
$n = bint($n);
$d = bint($d);
$d = $d/bgcd($n, $d);
return scalar (($d-bint(1)) << $b)/$d;
}
sub fmuls($$$) {
my($b,$n,$d) = @_;
my($s,$m);
my($thres) = bint(1) << ($b-1);
$n = bint($n);
$d = bint($d);
for ($s = 0; 1; $s++) {
$m = fmul($s,$n,$d);
return $s if ($m >= $thres);
}
return 0;
}
# Provides mul, adj, and shr factors for a specific
# (bit, time, hz) combination
sub muladj($$$) {
my($b, $t, $hz) = @_;
my $s = fmuls($b, $t, $hz);
my $m = fmul($s, $t, $hz);
my $a = fadj($s, $t, $hz);
return ($m->as_hex(), $a->as_hex(), $s);
}
# Provides numerator, denominator values
sub numden($$) {
my($n, $d) = @_;
my $g = bgcd($n, $d);
return ($n/$g, $d/$g);
}
# All values for a specific (time, hz) combo
sub conversions($$) {
my ($t, $hz) = @_;
my @val = ();
# HZ_TO_xx
push(@val, muladj(32, $t, $hz));
push(@val, muladj(64, $t, $hz));
push(@val, numden($t, $hz));
# xx_TO_HZ
push(@val, muladj(32, $hz, $t));
push(@val, muladj(64, $hz, $t));
push(@val, numden($hz, $t));
return @val;
}
sub compute_values($) {
my($hz) = @_;
my @val = ();
my $s, $m, $a, $g;
if (!$has_bigint) {
die "$0: HZ == $hz not canned and ".
"Math::BigInt not available\n";
}
# MSEC conversions
push(@val, conversions(1000, $hz));
# USEC conversions
push(@val, conversions(1000000, $hz));
return @val;
}
sub output($@)
{
my($hz, @val) = @_;
my $pfx, $bit, $suf, $s, $m, $a;
print "/* Automatically generated by kernel/timeconst.pl */\n";
print "/* Conversion constants for HZ == $hz */\n";
print "\n";
print "#ifndef KERNEL_TIMECONST_H\n";
print "#define KERNEL_TIMECONST_H\n";
print "\n";
print "#include <linux/param.h>\n";
print "\n";
print "#if HZ != $hz\n";
print "#error \"kernel/timeconst.h has the wrong HZ value!\"\n";
print "#endif\n";
print "\n";
foreach $pfx ('HZ_TO_MSEC','MSEC_TO_HZ',
'USEC_TO_HZ','HZ_TO_USEC') {
foreach $bit (32, 64) {
foreach $suf ('MUL', 'ADJ', 'SHR') {
printf "#define %-23s %s\n",
"${pfx}_$suf$bit", shift(@val);
}
}
foreach $suf ('NUM', 'DEN') {
printf "#define %-23s %s\n",
"${pfx}_$suf", shift(@val);
}
}
print "\n";
print "#endif /* KERNEL_TIMECONST_H */\n";
}
($hz) = @ARGV;
# Use this to generate the %canned_values structure
if ($hz eq '--can') {
shift(@ARGV);
@hzlist = sort {$a <=> $b} (@ARGV);
print "# Precomputed values for systems without Math::BigInt\n";
print "# Generated by:\n";
print "# timeconst.pl --can ", join(' ', @hzlist), "\n";
print "\%canned_values = (\n";
my $pf = "\t";
foreach $hz (@hzlist) {
my @values = compute_values($hz);
print "$pf$hz => [\n";
while (scalar(@values)) {
my $bit;
foreach $bit (32, 64) {
my $m = shift(@values);
my $a = shift(@values);
my $s = shift(@values);
print "\t\t\'",$m,"\',\'",$a,"\',",$s,",\n";
}
my $n = shift(@values);
my $d = shift(@values);
print "\t\t",$n,',',$d,",\n";
}
print "\t]";
$pf = ', ';
}
print "\n);\n";
} else {
$hz += 0; # Force to number
if ($hz < 1) {
die "Usage: $0 HZ\n";
}
@val = @{$canned_values{$hz}};
if (!defined(@val)) {
@val = compute_values($hz);
}
output($hz, @val);
}
exit 0;