bcachefs-tools/include/linux/math64.h

#ifndef _LINUX_MATH64_H
#define _LINUX_MATH64_H

#include <linux/types.h>

#define do_div(n,base) ({					\
	u32 __base = (base);					\
	u32 __rem;						\
	__rem = ((u64)(n)) % __base;				\
	(n) = ((u64)(n)) / __base;				\
	__rem;							\
 })

#define div64_long(x, y) div64_s64((x), (y))
#define div64_ul(x, y)   div64_u64((x), (y))

/**
 * div_u64_rem - unsigned 64bit divide with 32bit divisor with remainder
 *
 * This is commonly provided by 32bit archs to provide an optimized 64bit
 * divide.
 */
static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
{
	*remainder = dividend % divisor;
	return dividend / divisor;
}

/**
 * div_s64_rem - signed 64bit divide with 32bit divisor with remainder
 */
static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
{
	*remainder = dividend % divisor;
	return dividend / divisor;
}

/**
 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
 */
static inline u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
{
	*remainder = dividend % divisor;
	return dividend / divisor;
}

/**
 * div64_u64 - unsigned 64bit divide with 64bit divisor
 */
static inline u64 div64_u64(u64 dividend, u64 divisor)
{
	return dividend / divisor;
}

/**
 * div64_s64 - signed 64bit divide with 64bit divisor
 */
static inline s64 div64_s64(s64 dividend, s64 divisor)
{
	return dividend / divisor;
}

/**
 * div_u64 - unsigned 64bit divide with 32bit divisor
 *
 * This is the most common 64bit divide and should be used if possible,
 * as many 32bit archs can optimize this variant better than a full 64bit
 * divide.
 */
static inline u64 div_u64(u64 dividend, u32 divisor)
{
	u32 remainder;
	return div_u64_rem(dividend, divisor, &remainder);
}

/**
 * div_s64 - signed 64bit divide with 32bit divisor
 */
static inline s64 div_s64(s64 dividend, s32 divisor)
{
	s32 remainder;
	return div_s64_rem(dividend, divisor, &remainder);
}

#ifndef mul_u32_u32
/*
 * Many a GCC version messes this up and generates a 64x64 mult :-(
 */
static inline u64 mul_u32_u32(u32 a, u32 b)
{
	return (u64)a * b;
}
#endif

#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)

#ifndef mul_u64_u64_shr
static __always_inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int shift)
{
	return (u64)(((unsigned __int128)a * mul) >> shift);
}
#endif /* mul_u64_u64_shr */

#else

#ifndef mul_u64_u64_shr
static inline u64 mul_u64_u64_shr(u64 a, u64 b, unsigned int shift)
{
	union {
		u64 ll;
		struct {
#ifdef __BIG_ENDIAN
			u32 high, low;
#else
			u32 low, high;
#endif
		} l;
	} rl, rm, rn, rh, a0, b0;
	u64 c;

	a0.ll = a;
	b0.ll = b;

	rl.ll = mul_u32_u32(a0.l.low, b0.l.low);
	rm.ll = mul_u32_u32(a0.l.low, b0.l.high);
	rn.ll = mul_u32_u32(a0.l.high, b0.l.low);
	rh.ll = mul_u32_u32(a0.l.high, b0.l.high);

	/*
	 * Each of these lines computes a 64-bit intermediate result into "c",
	 * starting at bits 32-95.  The low 32-bits go into the result of the
	 * multiplication, the high 32-bits are carried into the next step.
	 */
	rl.l.high = c = (u64)rl.l.high + rm.l.low + rn.l.low;
	rh.l.low = c = (c >> 32) + rm.l.high + rn.l.high + rh.l.low;
	rh.l.high = (c >> 32) + rh.l.high;

	/*
	 * The 128-bit result of the multiplication is in rl.ll and rh.ll,
	 * shift it right and throw away the high part of the result.
	 */
	if (shift == 0)
		return rl.ll;
	if (shift < 64)
		return (rl.ll >> shift) | (rh.ll << (64 - shift));
	return rh.ll >> (shift & 63);
}
#endif /* mul_u64_u64_shr */

#endif

#endif /* _LINUX_MATH64_H */