* Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
* Based on former asm-ppc/div64.h and asm-m68knommu/div64.h
*
+ * Optimization for constant divisors on 32-bit machines:
+ * Copyright (C) 2006-2015 Nicolas Pitre
+ *
* The semantics of do_div() are:
*
- * uint32_t do_div(uint64_t *n, uint32_t base)
+ * u32 do_div(u64 *n, u32 base)
* {
- * uint32_t remainder = *n % base;
+ * u32 remainder = *n % base;
* *n = *n / base;
* return remainder;
* }
*/
#include <linux/types.h>
+#include <linux/compiler.h>
+
+#if BITS_PER_LONG == 64
+
+# define do_div(n,base) ({ \
+ u32 __base = (base); \
+ u32 __rem; \
+ __rem = ((u64)(n)) % __base; \
+ (n) = ((u64)(n)) / __base; \
+ __rem; \
+ })
+
+#elif BITS_PER_LONG == 32
+
+#include <linux/log2.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 which ought to be much faster. And yet only if compiling
+ * with a sufficiently recent gcc version to perform proper 64-bit constant
+ * propagation.
+ *
+ * (It is unfortunate that gcc doesn't perform all this internally.)
+ */
+
+#ifndef __div64_const32_is_OK
+#define __div64_const32_is_OK (__GNUC__ >= 4)
+#endif
+
+#define __div64_const32(n, ___b) \
+({ \
+ /* \
+ * Multiplication by reciprocal 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 few multiplication instructions should remain. \
+ * Hence this monstrous macro (static inline doesn't always \
+ * do the trick here). \
+ */ \
+ u64 ___res, ___x, ___t, ___m, ___n = (n); \
+ u32 ___p, ___bias; \
+ \
+ /* determine MSB of b */ \
+ ___p = 1 << ilog2(___b); \
+ \
+ /* compute m = ((p << 64) + b - 1) / b */ \
+ ___m = (~0ULL / ___b) * ___p; \
+ ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \
+ \
+ /* one less than the dividend with highest result */ \
+ ___x = ~0ULL / ___b * ___b - 1; \
+ \
+ /* test our ___m with res = m * x / (p << 64) */ \
+ ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32; \
+ ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \
+ ___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) { \
+ /* special case, can be simplified to ... */ \
+ ___n /= (___b & -___b); \
+ ___m = ~0ULL / (___b / (___b & -___b)); \
+ ___p = 1; \
+ ___bias = 1; \
+ } else if (___res != ___x / ___b) { \
+ /* \
+ * We can't get away without a bias to compensate \
+ * for bit truncation errors. To avoid it we'd need an \
+ * additional bit to represent m which would overflow \
+ * a 64-bit variable. \
+ * \
+ * Instead we do m = p / b and n / b = (n * m + m) / p. \
+ */ \
+ ___bias = 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. \
+ */ \
+ u32 ___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 >>= ilog2(___bits); \
+ ___m >>= ilog2(___bits); \
+ } \
+ /* No bias needed. */ \
+ ___bias = 0; \
+ } \
+ \
+ /* \
+ * Now we have a combination of 2 conditions: \
+ * \
+ * 1) whether or not we need to apply a bias, and \
+ * \
+ * 2) whether or not there might be an overflow in the cross \
+ * product determined by (___m & ((1 << 63) | (1 << 31))). \
+ * \
+ * Select the best way to do (m_bias + m * n) / (1 << 64). \
+ * From now on there will be actual runtime code generated. \
+ */ \
+ ___res = __arch_xprod_64(___m, ___n, ___bias); \
+ \
+ ___res /= ___p; \
+})
+
+#ifndef __arch_xprod_64
+/*
+ * Default C implementation for __arch_xprod_64()
+ *
+ * Prototype: u64 __arch_xprod_64(const u64 m, u64 n, bool bias)
+ * Semantic: retval = ((bias ? m : 0) + m * n) >> 64
+ *
+ * The product is a 128-bit value, scaled down to 64 bits.
+ * Assuming constant propagation to optimize away unused conditional code.
+ * Architectures may provide their own optimized assembly implementation.
+ */
+static inline u64 __arch_xprod_64(const u64 m, u64 n, bool bias)
+{
+ u32 m_lo = m;
+ u32 m_hi = m >> 32;
+ u32 n_lo = n;
+ u32 n_hi = n >> 32;
+ u64 res, tmp;
+
+ if (!bias) {
+ res = ((u64)m_lo * n_lo) >> 32;
+ } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+ /* there can't be any overflow here */
+ res = (m + (u64)m_lo * n_lo) >> 32;
+ } else {
+ res = m + (u64)m_lo * n_lo;
+ tmp = (res < m) ? (1ULL << 32) : 0;
+ res = (res >> 32) + tmp;
+ }
+
+ if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+ /* there can't be any overflow here */
+ res += (u64)m_lo * n_hi;
+ res += (u64)m_hi * n_lo;
+ res >>= 32;
+ } else {
+ tmp = res += (u64)m_lo * n_hi;
+ res += (u64)m_hi * n_lo;
+ tmp = (res < tmp) ? (1ULL << 32) : 0;
+ res = (res >> 32) + tmp;
+ }
-extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
+ res += (u64)m_hi * n_hi;
+
+ return res;
+}
+#endif
+
+#ifndef __div64_32
+extern u32 __div64_32(u64 *dividend, u32 divisor);
+#endif
/* The unnecessary pointer compare is there
* to check for type safety (n must be 64bit)
*/
# define do_div(n,base) ({ \
- uint32_t __base = (base); \
- uint32_t __rem; \
- (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
- if (((n) >> 32) == 0) { \
- __rem = (uint32_t)(n) % __base; \
- (n) = (uint32_t)(n) / __base; \
- } else \
+ u32 __base = (base); \
+ u32 __rem; \
+ (void)(((typeof((n)) *)0) == ((u64 *)0)); \
+ if (__builtin_constant_p(__base) && \
+ is_power_of_2(__base)) { \
+ __rem = (n) & (__base - 1); \
+ (n) >>= ilog2(__base); \
+ } else if (__div64_const32_is_OK && \
+ __builtin_constant_p(__base) && \
+ __base != 0) { \
+ u32 __res_lo, __n_lo = (n); \
+ (n) = __div64_const32(n, __base); \
+ /* the remainder can be computed with 32-bit regs */ \
+ __res_lo = (n); \
+ __rem = __n_lo - __res_lo * __base; \
+ } else if (likely(((n) >> 32) == 0)) { \
+ __rem = (u32)(n) % __base; \
+ (n) = (u32)(n) / __base; \
+ } else \
__rem = __div64_32(&(n), __base); \
__rem; \
})
+#else /* BITS_PER_LONG == ?? */
+
+# error do_div() does not yet support the C64
+
+#endif /* BITS_PER_LONG */
+
/* Wrapper for do_div(). Doesn't modify dividend and returns
- * the result, not reminder.
+ * the result, not remainder.
*/
-static inline uint64_t lldiv(uint64_t dividend, uint32_t divisor)
+static inline u64 lldiv(u64 dividend, u32 divisor)
{
- uint64_t __res = dividend;
+ u64 __res = dividend;
do_div(__res, divisor);
return(__res);
}
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