linux/include/asm-arm/div64.h
Roman Zippel 6f6d6a1a6a rename div64_64 to div64_u64
Rename div64_64 to div64_u64 to make it consistent with the other divide
functions, so it clearly includes the type of the divide.  Move its definition
to math64.h as currently no architecture overrides the generic implementation.
 They can still override it of course, but the duplicated declarations are
avoided.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Cc: Avi Kivity <avi@qumranet.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-01 08:03:58 -07:00

227 lines
7.5 KiB
C

#ifndef __ASM_ARM_DIV64
#define __ASM_ARM_DIV64
#include <asm/system.h>
#include <linux/types.h>
/*
* The semantics of do_div() are:
*
* uint32_t do_div(uint64_t *n, uint32_t base)
* {
* uint32_t remainder = *n % base;
* *n = *n / base;
* return remainder;
* }
*
* In other words, a 64-bit dividend with a 32-bit divisor producing
* a 64-bit result and a 32-bit remainder. To accomplish this optimally
* we call a special __do_div64 helper with completely non standard
* calling convention for arguments and results (beware).
*/
#ifdef __ARMEB__
#define __xh "r0"
#define __xl "r1"
#else
#define __xl "r0"
#define __xh "r1"
#endif
#define __do_div_asm(n, base) \
({ \
register unsigned int __base asm("r4") = base; \
register unsigned long long __n asm("r0") = n; \
register unsigned long long __res asm("r2"); \
register unsigned int __rem asm(__xh); \
asm( __asmeq("%0", __xh) \
__asmeq("%1", "r2") \
__asmeq("%2", "r0") \
__asmeq("%3", "r4") \
"bl __do_div64" \
: "=r" (__rem), "=r" (__res) \
: "r" (__n), "r" (__base) \
: "ip", "lr", "cc"); \
n = __res; \
__rem; \
})
#if __GNUC__ < 4
/*
* gcc versions earlier than 4.0 are simply too problematic for the
* optimized implementation below. First there is gcc PR 15089 that
* tend to trig on more complex constructs, spurious .global __udivsi3
* are inserted even if none of those symbols are referenced in the
* generated code, and those gcc versions are not able to do constant
* propagation on long long values anyway.
*/
#define do_div(n, base) __do_div_asm(n, base)
#elif __GNUC__ >= 4
#include <asm/bug.h>
/*
* If the divisor happens to be constant, we determine the appropriate
* inverse at compile time to turn the division into a few inline
* multiplications instead which is much faster. And yet only if compiling
* for ARMv4 or higher (we need umull/umlal) and if the gcc version is
* sufficiently recent to perform proper long long constant propagation.
* (It is unfortunate that gcc doesn't perform all this internally.)
*/
#define do_div(n, base) \
({ \
unsigned int __r, __b = (base); \
if (!__builtin_constant_p(__b) || __b == 0 || \
(__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) { \
/* non-constant divisor (or zero): slow path */ \
__r = __do_div_asm(n, __b); \
} else if ((__b & (__b - 1)) == 0) { \
/* Trivial: __b is constant and a power of 2 */ \
/* gcc does the right thing with this code. */ \
__r = n; \
__r &= (__b - 1); \
n /= __b; \
} else { \
/* Multiply by inverse of __b: n/b = n*(p/b)/p */ \
/* We rely on the fact that most of this code gets */ \
/* optimized away at compile time due to constant */ \
/* propagation and only a couple inline assembly */ \
/* instructions should remain. Better avoid any */ \
/* code construct that might prevent that. */ \
unsigned long long __res, __x, __t, __m, __n = n; \
unsigned int __c, __p, __z = 0; \
/* preserve low part of n for reminder computation */ \
__r = __n; \
/* determine number of bits to represent __b */ \
__p = 1 << __div64_fls(__b); \
/* compute __m = ((__p << 64) + __b - 1) / __b */ \
__m = (~0ULL / __b) * __p; \
__m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b; \
/* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */ \
__x = ~0ULL / __b * __b - 1; \
__res = (__m & 0xffffffff) * (__x & 0xffffffff); \
__res >>= 32; \
__res += (__m & 0xffffffff) * (__x >> 32); \
__t = __res; \
__res += (__x & 0xffffffff) * (__m >> 32); \
__t = (__res < __t) ? (1ULL << 32) : 0; \
__res = (__res >> 32) + __t; \
__res += (__m >> 32) * (__x >> 32); \
__res /= __p; \
/* Now sanitize and optimize what we've got. */ \
if (~0ULL % (__b / (__b & -__b)) == 0) { \
/* those cases can be simplified with: */ \
__n /= (__b & -__b); \
__m = ~0ULL / (__b / (__b & -__b)); \
__p = 1; \
__c = 1; \
} else if (__res != __x / __b) { \
/* We can't get away without a correction */ \
/* to compensate for bit truncation errors. */ \
/* To avoid it we'd need an additional bit */ \
/* to represent __m which would overflow it. */ \
/* Instead we do m=p/b and n/b=(n*m+m)/p. */ \
__c = 1; \
/* Compute __m = (__p << 64) / __b */ \
__m = (~0ULL / __b) * __p; \
__m += ((~0ULL % __b + 1) * __p) / __b; \
} else { \
/* Reduce __m/__p, and try to clear bit 31 */ \
/* of __m when possible otherwise that'll */ \
/* need extra overflow handling later. */ \
unsigned int __bits = -(__m & -__m); \
__bits |= __m >> 32; \
__bits = (~__bits) << 1; \
/* If __bits == 0 then setting bit 31 is */ \
/* unavoidable. Simply apply the maximum */ \
/* possible reduction in that case. */ \
/* Otherwise the MSB of __bits indicates the */ \
/* best reduction we should apply. */ \
if (!__bits) { \
__p /= (__m & -__m); \
__m /= (__m & -__m); \
} else { \
__p >>= __div64_fls(__bits); \
__m >>= __div64_fls(__bits); \
} \
/* No correction needed. */ \
__c = 0; \
} \
/* Now we have a combination of 2 conditions: */ \
/* 1) whether or not we need a correction (__c), and */ \
/* 2) whether or not there might be an overflow in */ \
/* the cross product (__m & ((1<<63) | (1<<31))) */ \
/* Select the best insn combination to perform the */ \
/* actual __m * __n / (__p << 64) operation. */ \
if (!__c) { \
asm ( "umull %Q0, %R0, %1, %Q2\n\t" \
"mov %Q0, #0" \
: "=&r" (__res) \
: "r" (__m), "r" (__n) \
: "cc" ); \
} else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
__res = __m; \
asm ( "umlal %Q0, %R0, %Q1, %Q2\n\t" \
"mov %Q0, #0" \
: "+r" (__res) \
: "r" (__m), "r" (__n) \
: "cc" ); \
} else { \
asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \
"cmn %Q0, %Q1\n\t" \
"adcs %R0, %R0, %R1\n\t" \
"adc %Q0, %3, #0" \
: "=&r" (__res) \
: "r" (__m), "r" (__n), "r" (__z) \
: "cc" ); \
} \
if (!(__m & ((1ULL << 63) | (1ULL << 31)))) { \
asm ( "umlal %R0, %Q0, %R1, %Q2\n\t" \
"umlal %R0, %Q0, %Q1, %R2\n\t" \
"mov %R0, #0\n\t" \
"umlal %Q0, %R0, %R1, %R2" \
: "+r" (__res) \
: "r" (__m), "r" (__n) \
: "cc" ); \
} else { \
asm ( "umlal %R0, %Q0, %R2, %Q3\n\t" \
"umlal %R0, %1, %Q2, %R3\n\t" \
"mov %R0, #0\n\t" \
"adds %Q0, %1, %Q0\n\t" \
"adc %R0, %R0, #0\n\t" \
"umlal %Q0, %R0, %R2, %R3" \
: "+r" (__res), "+r" (__z) \
: "r" (__m), "r" (__n) \
: "cc" ); \
} \
__res /= __p; \
/* The reminder can be computed with 32-bit regs */ \
/* only, and gcc is good at that. */ \
{ \
unsigned int __res0 = __res; \
unsigned int __b0 = __b; \
__r -= __res0 * __b0; \
} \
/* BUG_ON(__r >= __b || __res * __b + __r != n); */ \
n = __res; \
} \
__r; \
})
/* our own fls implementation to make sure constant propagation is fine */
#define __div64_fls(bits) \
({ \
unsigned int __left = (bits), __nr = 0; \
if (__left & 0xffff0000) __nr += 16, __left >>= 16; \
if (__left & 0x0000ff00) __nr += 8, __left >>= 8; \
if (__left & 0x000000f0) __nr += 4, __left >>= 4; \
if (__left & 0x0000000c) __nr += 2, __left >>= 2; \
if (__left & 0x00000002) __nr += 1; \
__nr; \
})
#endif
#endif