#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 extern uint64_t div64_64(uint64_t dividend, uint64_t divisor); #endif