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libdivide.h
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libdivide.h
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// libdivide.h - Optimized integer division
// https://libdivide.com
//
// Copyright (C) 2010 - 2021 ridiculous_fish, <libdivide@ridiculousfish.com>
// Copyright (C) 2016 - 2021 Kim Walisch, <kim.walisch@gmail.com>
//
// libdivide is dual-licensed under the Boost or zlib licenses.
// You may use libdivide under the terms of either of these.
// See LICENSE.txt for more details.
#ifndef LIBDIVIDE_H
#define LIBDIVIDE_H
#define LIBDIVIDE_VERSION "5.0"
#define LIBDIVIDE_VERSION_MAJOR 5
#define LIBDIVIDE_VERSION_MINOR 0
#include <stdint.h>
#if !defined(__AVR__)
#include <stdio.h>
#include <stdlib.h>
#endif
#if defined(LIBDIVIDE_SSE2)
#include <emmintrin.h>
#endif
#if defined(LIBDIVIDE_AVX2) || defined(LIBDIVIDE_AVX512)
#include <immintrin.h>
#endif
#if defined(LIBDIVIDE_NEON)
#include <arm_neon.h>
#endif
#if defined(_MSC_VER)
#include <intrin.h>
#pragma warning(push)
// disable warning C4146: unary minus operator applied
// to unsigned type, result still unsigned
#pragma warning(disable : 4146)
// disable warning C4204: nonstandard extension used : non-constant aggregate
// initializer
//
// It's valid C99
#pragma warning(disable : 4204)
#define LIBDIVIDE_VC
#endif
#if !defined(__has_builtin)
#define __has_builtin(x) 0
#endif
#if defined(__SIZEOF_INT128__)
#define HAS_INT128_T
// clang-cl on Windows does not yet support 128-bit division
#if !(defined(__clang__) && defined(LIBDIVIDE_VC))
#define HAS_INT128_DIV
#endif
#endif
#if defined(__x86_64__) || defined(_M_X64)
#define LIBDIVIDE_X86_64
#endif
#if defined(__i386__)
#define LIBDIVIDE_i386
#endif
#if defined(__GNUC__) || defined(__clang__)
#define LIBDIVIDE_GCC_STYLE_ASM
#endif
#if defined(__cplusplus) || defined(LIBDIVIDE_VC)
#define LIBDIVIDE_FUNCTION __FUNCTION__
#else
#define LIBDIVIDE_FUNCTION __func__
#endif
// Set up forced inlining if possible.
// We need both the attribute and keyword to avoid "might not be inlineable" warnings.
#ifdef __has_attribute
#if __has_attribute(always_inline)
#define LIBDIVIDE_INLINE __attribute__((always_inline)) inline
#endif
#endif
#ifndef LIBDIVIDE_INLINE
#define LIBDIVIDE_INLINE inline
#endif
#if defined(__AVR__)
#define LIBDIVIDE_ERROR(msg)
#else
#define LIBDIVIDE_ERROR(msg) \
do { \
fprintf(stderr, "libdivide.h:%d: %s(): Error: %s\n", __LINE__, LIBDIVIDE_FUNCTION, msg); \
abort(); \
} while (0)
#endif
#if defined(LIBDIVIDE_ASSERTIONS_ON) && !defined(__AVR__)
#define LIBDIVIDE_ASSERT(x) \
do { \
if (!(x)) { \
fprintf(stderr, "libdivide.h:%d: %s(): Assertion failed: %s\n", __LINE__, \
LIBDIVIDE_FUNCTION, #x); \
abort(); \
} \
} while (0)
#else
#define LIBDIVIDE_ASSERT(x)
#endif
#ifdef __cplusplus
namespace libdivide
{
#endif
// pack divider structs to prevent compilers from padding.
// This reduces memory usage by up to 43% when using a large
// array of libdivide dividers and improves performance
// by up to 10% because of reduced memory bandwidth.
#pragma pack(push, 1)
struct libdivide_u16_t
{
uint16_t magic;
uint8_t more;
};
struct libdivide_s16_t
{
int16_t magic;
uint8_t more;
};
struct libdivide_u32_t
{
uint32_t magic;
uint8_t more;
};
struct libdivide_s32_t
{
int32_t magic;
uint8_t more;
};
struct libdivide_u64_t
{
uint64_t magic;
uint8_t more;
};
struct libdivide_s64_t
{
int64_t magic;
uint8_t more;
};
struct libdivide_u16_branchfree_t
{
uint16_t magic;
uint8_t more;
};
struct libdivide_s16_branchfree_t
{
int16_t magic;
uint8_t more;
};
struct libdivide_u32_branchfree_t
{
uint32_t magic;
uint8_t more;
};
struct libdivide_s32_branchfree_t
{
int32_t magic;
uint8_t more;
};
struct libdivide_u64_branchfree_t
{
uint64_t magic;
uint8_t more;
};
struct libdivide_s64_branchfree_t
{
int64_t magic;
uint8_t more;
};
#pragma pack(pop)
// Explanation of the "more" field:
//
// * Bits 0-5 is the shift value (for shift path or mult path).
// * Bit 6 is the add indicator for mult path.
// * Bit 7 is set if the divisor is negative. We use bit 7 as the negative
// divisor indicator so that we can efficiently use sign extension to
// create a bitmask with all bits set to 1 (if the divisor is negative)
// or 0 (if the divisor is positive).
//
// u32: [0-4] shift value
// [5] ignored
// [6] add indicator
// magic number of 0 indicates shift path
//
// s32: [0-4] shift value
// [5] ignored
// [6] add indicator
// [7] indicates negative divisor
// magic number of 0 indicates shift path
//
// u64: [0-5] shift value
// [6] add indicator
// magic number of 0 indicates shift path
//
// s64: [0-5] shift value
// [6] add indicator
// [7] indicates negative divisor
// magic number of 0 indicates shift path
//
// In s32 and s64 branchfree modes, the magic number is negated according to
// whether the divisor is negated. In branchfree strategy, it is not negated.
enum
{
LIBDIVIDE_16_SHIFT_MASK = 0x1F,
LIBDIVIDE_32_SHIFT_MASK = 0x1F,
LIBDIVIDE_64_SHIFT_MASK = 0x3F,
LIBDIVIDE_ADD_MARKER = 0x40,
LIBDIVIDE_NEGATIVE_DIVISOR = 0x80
};
static LIBDIVIDE_INLINE struct libdivide_s16_t libdivide_s16_gen(int16_t d);
static LIBDIVIDE_INLINE struct libdivide_u16_t libdivide_u16_gen(uint16_t d);
static LIBDIVIDE_INLINE struct libdivide_s32_t libdivide_s32_gen(int32_t d);
static LIBDIVIDE_INLINE struct libdivide_u32_t libdivide_u32_gen(uint32_t d);
static LIBDIVIDE_INLINE struct libdivide_s64_t libdivide_s64_gen(int64_t d);
static LIBDIVIDE_INLINE struct libdivide_u64_t libdivide_u64_gen(uint64_t d);
static LIBDIVIDE_INLINE struct libdivide_s16_branchfree_t libdivide_s16_branchfree_gen(int16_t d);
static LIBDIVIDE_INLINE struct libdivide_u16_branchfree_t libdivide_u16_branchfree_gen(uint16_t d);
static LIBDIVIDE_INLINE struct libdivide_s32_branchfree_t libdivide_s32_branchfree_gen(int32_t d);
static LIBDIVIDE_INLINE struct libdivide_u32_branchfree_t libdivide_u32_branchfree_gen(uint32_t d);
static LIBDIVIDE_INLINE struct libdivide_s64_branchfree_t libdivide_s64_branchfree_gen(int64_t d);
static LIBDIVIDE_INLINE struct libdivide_u64_branchfree_t libdivide_u64_branchfree_gen(uint64_t d);
static LIBDIVIDE_INLINE int16_t libdivide_s16_do_raw(int16_t numer, int16_t magic, uint8_t more);
static LIBDIVIDE_INLINE int16_t libdivide_s16_do(
int16_t numer, const struct libdivide_s16_t *denom);
static LIBDIVIDE_INLINE uint16_t libdivide_u16_do_raw(uint16_t numer, uint16_t magic, uint8_t more);
static LIBDIVIDE_INLINE uint16_t libdivide_u16_do(
uint16_t numer, const struct libdivide_u16_t *denom);
static LIBDIVIDE_INLINE int32_t libdivide_s32_do(
int32_t numer, const struct libdivide_s32_t *denom);
static LIBDIVIDE_INLINE uint32_t libdivide_u32_do(
uint32_t numer, const struct libdivide_u32_t *denom);
static LIBDIVIDE_INLINE int64_t libdivide_s64_do(
int64_t numer, const struct libdivide_s64_t *denom);
static LIBDIVIDE_INLINE uint64_t libdivide_u64_do(
uint64_t numer, const struct libdivide_u64_t *denom);
static LIBDIVIDE_INLINE int16_t libdivide_s16_branchfree_do(
int16_t numer, const struct libdivide_s16_branchfree_t *denom);
static LIBDIVIDE_INLINE uint16_t libdivide_u16_branchfree_do(
uint16_t numer, const struct libdivide_u16_branchfree_t *denom);
static LIBDIVIDE_INLINE int32_t libdivide_s32_branchfree_do(
int32_t numer, const struct libdivide_s32_branchfree_t *denom);
static LIBDIVIDE_INLINE uint32_t libdivide_u32_branchfree_do(
uint32_t numer, const struct libdivide_u32_branchfree_t *denom);
static LIBDIVIDE_INLINE int64_t libdivide_s64_branchfree_do(
int64_t numer, const struct libdivide_s64_branchfree_t *denom);
static LIBDIVIDE_INLINE uint64_t libdivide_u64_branchfree_do(
uint64_t numer, const struct libdivide_u64_branchfree_t *denom);
static LIBDIVIDE_INLINE int16_t libdivide_s16_recover(const struct libdivide_s16_t *denom);
static LIBDIVIDE_INLINE uint16_t libdivide_u16_recover(const struct libdivide_u16_t *denom);
static LIBDIVIDE_INLINE int32_t libdivide_s32_recover(const struct libdivide_s32_t *denom);
static LIBDIVIDE_INLINE uint32_t libdivide_u32_recover(const struct libdivide_u32_t *denom);
static LIBDIVIDE_INLINE int64_t libdivide_s64_recover(const struct libdivide_s64_t *denom);
static LIBDIVIDE_INLINE uint64_t libdivide_u64_recover(const struct libdivide_u64_t *denom);
static LIBDIVIDE_INLINE int16_t libdivide_s16_branchfree_recover(
const struct libdivide_s16_branchfree_t *denom);
static LIBDIVIDE_INLINE uint16_t libdivide_u16_branchfree_recover(
const struct libdivide_u16_branchfree_t *denom);
static LIBDIVIDE_INLINE int32_t libdivide_s32_branchfree_recover(
const struct libdivide_s32_branchfree_t *denom);
static LIBDIVIDE_INLINE uint32_t libdivide_u32_branchfree_recover(
const struct libdivide_u32_branchfree_t *denom);
static LIBDIVIDE_INLINE int64_t libdivide_s64_branchfree_recover(
const struct libdivide_s64_branchfree_t *denom);
static LIBDIVIDE_INLINE uint64_t libdivide_u64_branchfree_recover(
const struct libdivide_u64_branchfree_t *denom);
//////// Internal Utility Functions
static LIBDIVIDE_INLINE uint16_t libdivide_mullhi_u16(uint16_t x, uint16_t y)
{
uint32_t xl = x, yl = y;
uint32_t rl = xl * yl;
return (uint16_t)(rl >> 16);
}
static LIBDIVIDE_INLINE int16_t libdivide_mullhi_s16(int16_t x, int16_t y)
{
int32_t xl = x, yl = y;
int32_t rl = xl * yl;
// needs to be arithmetic shift
return (int16_t)(rl >> 16);
}
static LIBDIVIDE_INLINE uint32_t libdivide_mullhi_u32(uint32_t x, uint32_t y)
{
uint64_t xl = x, yl = y;
uint64_t rl = xl * yl;
return (uint32_t)(rl >> 32);
}
static LIBDIVIDE_INLINE int32_t libdivide_mullhi_s32(int32_t x, int32_t y)
{
int64_t xl = x, yl = y;
int64_t rl = xl * yl;
// needs to be arithmetic shift
return (int32_t)(rl >> 32);
}
static LIBDIVIDE_INLINE uint64_t libdivide_mullhi_u64(uint64_t x, uint64_t y)
{
#if defined(LIBDIVIDE_VC) && defined(LIBDIVIDE_X86_64)
return __umulh(x, y);
#elif defined(HAS_INT128_T)
__uint128_t xl = x, yl = y;
__uint128_t rl = xl * yl;
return (uint64_t)(rl >> 64);
#else
// full 128 bits are x0 * y0 + (x0 * y1 << 32) + (x1 * y0 << 32) + (x1 * y1 << 64)
uint32_t mask = 0xFFFFFFFF;
uint32_t x0 = (uint32_t)(x & mask);
uint32_t x1 = (uint32_t)(x >> 32);
uint32_t y0 = (uint32_t)(y & mask);
uint32_t y1 = (uint32_t)(y >> 32);
uint32_t x0y0_hi = libdivide_mullhi_u32(x0, y0);
uint64_t x0y1 = x0 * (uint64_t)y1;
uint64_t x1y0 = x1 * (uint64_t)y0;
uint64_t x1y1 = x1 * (uint64_t)y1;
uint64_t temp = x1y0 + x0y0_hi;
uint64_t temp_lo = temp & mask;
uint64_t temp_hi = temp >> 32;
return x1y1 + temp_hi + ((temp_lo + x0y1) >> 32);
#endif
}
static LIBDIVIDE_INLINE int64_t libdivide_mullhi_s64(int64_t x, int64_t y)
{
#if defined(LIBDIVIDE_VC) && defined(LIBDIVIDE_X86_64)
return __mulh(x, y);
#elif defined(HAS_INT128_T)
__int128_t xl = x, yl = y;
__int128_t rl = xl * yl;
return (int64_t)(rl >> 64);
#else
// full 128 bits are x0 * y0 + (x0 * y1 << 32) + (x1 * y0 << 32) + (x1 * y1 << 64)
uint32_t mask = 0xFFFFFFFF;
uint32_t x0 = (uint32_t)(x & mask);
uint32_t y0 = (uint32_t)(y & mask);
int32_t x1 = (int32_t)(x >> 32);
int32_t y1 = (int32_t)(y >> 32);
uint32_t x0y0_hi = libdivide_mullhi_u32(x0, y0);
int64_t t = x1 * (int64_t)y0 + x0y0_hi;
int64_t w1 = x0 * (int64_t)y1 + (t & mask);
return x1 * (int64_t)y1 + (t >> 32) + (w1 >> 32);
#endif
}
static LIBDIVIDE_INLINE int16_t libdivide_count_leading_zeros16(uint16_t val)
{
#if defined(__AVR__)
// Fast way to count leading zeros
// On the AVR 8-bit architecture __builtin_clz() works on a int16_t.
return __builtin_clz(val);
#elif defined(__GNUC__) || __has_builtin(__builtin_clz)
// Fast way to count leading zeros
return __builtin_clz(val) - 16;
#elif defined(LIBDIVIDE_VC)
unsigned long result;
if (_BitScanReverse(&result, (unsigned long)val))
{
return (int16_t)(15 - result);
}
return 0;
#else
if (val == 0) return 16;
int16_t result = 4;
uint16_t hi = 0xFU << 12;
while ((val & hi) == 0)
{
hi >>= 4;
result += 4;
}
while (val & hi)
{
result -= 1;
hi <<= 1;
}
return result;
#endif
}
static LIBDIVIDE_INLINE int32_t libdivide_count_leading_zeros32(uint32_t val)
{
#if defined(__AVR__)
// Fast way to count leading zeros
return __builtin_clzl(val);
#elif defined(__GNUC__) || __has_builtin(__builtin_clz)
// Fast way to count leading zeros
return __builtin_clz(val);
#elif defined(LIBDIVIDE_VC)
unsigned long result;
if (_BitScanReverse(&result, val))
{
return 31 - result;
}
return 0;
#else
if (val == 0) return 32;
int32_t result = 8;
uint32_t hi = 0xFFU << 24;
while ((val & hi) == 0)
{
hi >>= 8;
result += 8;
}
while (val & hi)
{
result -= 1;
hi <<= 1;
}
return result;
#endif
}
static LIBDIVIDE_INLINE int32_t libdivide_count_leading_zeros64(uint64_t val)
{
#if defined(__GNUC__) || __has_builtin(__builtin_clzll)
// Fast way to count leading zeros
return __builtin_clzll(val);
#elif defined(LIBDIVIDE_VC) && defined(_WIN64)
unsigned long result;
if (_BitScanReverse64(&result, val))
{
return 63 - result;
}
return 0;
#else
uint32_t hi = val >> 32;
uint32_t lo = val & 0xFFFFFFFF;
if (hi != 0) return libdivide_count_leading_zeros32(hi);
return 32 + libdivide_count_leading_zeros32(lo);
#endif
}
// libdivide_32_div_16_to_16: divides a 32-bit uint {u1, u0} by a 16-bit
// uint {v}. The result must fit in 16 bits.
// Returns the quotient directly and the remainder in *r
static LIBDIVIDE_INLINE uint16_t libdivide_32_div_16_to_16(
uint16_t u1, uint16_t u0, uint16_t v, uint16_t *r)
{
uint32_t n = ((uint32_t)u1 << 16) | u0;
uint16_t result = (uint16_t)(n / v);
*r = (uint16_t)(n - result * (uint32_t)v);
return result;
}
// libdivide_64_div_32_to_32: divides a 64-bit uint {u1, u0} by a 32-bit
// uint {v}. The result must fit in 32 bits.
// Returns the quotient directly and the remainder in *r
static LIBDIVIDE_INLINE uint32_t libdivide_64_div_32_to_32(
uint32_t u1, uint32_t u0, uint32_t v, uint32_t *r)
{
#if (defined(LIBDIVIDE_i386) || defined(LIBDIVIDE_X86_64)) && defined(LIBDIVIDE_GCC_STYLE_ASM)
uint32_t result;
__asm__("divl %[v]" : "=a"(result), "=d"(*r) : [v] "r"(v), "a"(u0), "d"(u1));
return result;
#else
uint64_t n = ((uint64_t)u1 << 32) | u0;
uint32_t result = (uint32_t)(n / v);
*r = (uint32_t)(n - result * (uint64_t)v);
return result;
#endif
}
// libdivide_128_div_64_to_64: divides a 128-bit uint {numhi, numlo} by a 64-bit uint {den}. The
// result must fit in 64 bits. Returns the quotient directly and the remainder in *r
static LIBDIVIDE_INLINE uint64_t libdivide_128_div_64_to_64(
uint64_t numhi, uint64_t numlo, uint64_t den, uint64_t *r)
{
// N.B. resist the temptation to use __uint128_t here.
// In LLVM compiler-rt, it performs a 128/128 -> 128 division which is many times slower than
// necessary. In gcc it's better but still slower than the divlu implementation, perhaps because
// it's not LIBDIVIDE_INLINEd.
#if defined(LIBDIVIDE_X86_64) && defined(LIBDIVIDE_GCC_STYLE_ASM)
uint64_t result;
__asm__("divq %[v]" : "=a"(result), "=d"(*r) : [v] "r"(den), "a"(numlo), "d"(numhi));
return result;
#else
// We work in base 2**32.
// A uint32 holds a single digit. A uint64 holds two digits.
// Our numerator is conceptually [num3, num2, num1, num0].
// Our denominator is [den1, den0].
const uint64_t b = ((uint64_t)1 << 32);
// The high and low digits of our computed quotient.
uint32_t q1;
uint32_t q0;
// The normalization shift factor.
int shift;
// The high and low digits of our denominator (after normalizing).
// Also the low 2 digits of our numerator (after normalizing).
uint32_t den1;
uint32_t den0;
uint32_t num1;
uint32_t num0;
// A partial remainder.
uint64_t rem;
// The estimated quotient, and its corresponding remainder (unrelated to true remainder).
uint64_t qhat;
uint64_t rhat;
// Variables used to correct the estimated quotient.
uint64_t c1;
uint64_t c2;
// Check for overflow and divide by 0.
if (numhi >= den)
{
if (r != NULL) *r = ~0ull;
return ~0ull;
}
// Determine the normalization factor. We multiply den by this, so that its leading digit is at
// least half b. In binary this means just shifting left by the number of leading zeros, so that
// there's a 1 in the MSB.
// We also shift numer by the same amount. This cannot overflow because numhi < den.
// The expression (-shift & 63) is the same as (64 - shift), except it avoids the UB of shifting
// by 64. The funny bitwise 'and' ensures that numlo does not get shifted into numhi if shift is
// 0. clang 11 has an x86 codegen bug here: see LLVM bug 50118. The sequence below avoids it.
shift = libdivide_count_leading_zeros64(den);
den <<= shift;
numhi <<= shift;
numhi |= (numlo >> (-shift & 63)) & (-(int64_t)shift >> 63);
numlo <<= shift;
// Extract the low digits of the numerator and both digits of the denominator.
num1 = (uint32_t)(numlo >> 32);
num0 = (uint32_t)(numlo & 0xFFFFFFFFu);
den1 = (uint32_t)(den >> 32);
den0 = (uint32_t)(den & 0xFFFFFFFFu);
// We wish to compute q1 = [n3 n2 n1] / [d1 d0].
// Estimate q1 as [n3 n2] / [d1], and then correct it.
// Note while qhat may be 2 digits, q1 is always 1 digit.
qhat = numhi / den1;
rhat = numhi % den1;
c1 = qhat * den0;
c2 = rhat * b + num1;
if (c1 > c2) qhat -= (c1 - c2 > den) ? 2 : 1;
q1 = (uint32_t)qhat;
// Compute the true (partial) remainder.
rem = numhi * b + num1 - q1 * den;
// We wish to compute q0 = [rem1 rem0 n0] / [d1 d0].
// Estimate q0 as [rem1 rem0] / [d1] and correct it.
qhat = rem / den1;
rhat = rem % den1;
c1 = qhat * den0;
c2 = rhat * b + num0;
if (c1 > c2) qhat -= (c1 - c2 > den) ? 2 : 1;
q0 = (uint32_t)qhat;
// Return remainder if requested.
if (r != NULL) *r = (rem * b + num0 - q0 * den) >> shift;
return ((uint64_t)q1 << 32) | q0;
#endif
}
// Bitshift a u128 in place, left (signed_shift > 0) or right (signed_shift < 0)
static LIBDIVIDE_INLINE void libdivide_u128_shift(
uint64_t *u1, uint64_t *u0, int32_t signed_shift)
{
if (signed_shift > 0)
{
uint32_t shift = signed_shift;
*u1 <<= shift;
*u1 |= *u0 >> (64 - shift);
*u0 <<= shift;
}
else if (signed_shift < 0)
{
uint32_t shift = -signed_shift;
*u0 >>= shift;
*u0 |= *u1 << (64 - shift);
*u1 >>= shift;
}
}
// Computes a 128 / 128 -> 64 bit division, with a 128 bit remainder.
static LIBDIVIDE_INLINE uint64_t libdivide_128_div_128_to_64(
uint64_t u_hi, uint64_t u_lo, uint64_t v_hi, uint64_t v_lo, uint64_t *r_hi, uint64_t *r_lo)
{
#if defined(HAS_INT128_T) && defined(HAS_INT128_DIV)
__uint128_t ufull = u_hi;
__uint128_t vfull = v_hi;
ufull = (ufull << 64) | u_lo;
vfull = (vfull << 64) | v_lo;
uint64_t res = (uint64_t)(ufull / vfull);
__uint128_t remainder = ufull - (vfull * res);
*r_lo = (uint64_t)remainder;
*r_hi = (uint64_t)(remainder >> 64);
return res;
#else
// Adapted from "Unsigned Doubleword Division" in Hacker's Delight
// We want to compute u / v
typedef struct
{
uint64_t hi;
uint64_t lo;
} u128_t;
u128_t u = {u_hi, u_lo};
u128_t v = {v_hi, v_lo};
if (v.hi == 0)
{
// divisor v is a 64 bit value, so we just need one 128/64 division
// Note that we are simpler than Hacker's Delight here, because we know
// the quotient fits in 64 bits whereas Hacker's Delight demands a full
// 128 bit quotient
*r_hi = 0;
return libdivide_128_div_64_to_64(u.hi, u.lo, v.lo, r_lo);
}
// Here v >= 2**64
// We know that v.hi != 0, so count leading zeros is OK
// We have 0 <= n <= 63
uint32_t n = libdivide_count_leading_zeros64(v.hi);
// Normalize the divisor so its MSB is 1
u128_t v1t = v;
libdivide_u128_shift(&v1t.hi, &v1t.lo, n);
uint64_t v1 = v1t.hi; // i.e. v1 = v1t >> 64
// To ensure no overflow
u128_t u1 = u;
libdivide_u128_shift(&u1.hi, &u1.lo, -1);
// Get quotient from divide unsigned insn.
uint64_t rem_ignored;
uint64_t q1 = libdivide_128_div_64_to_64(u1.hi, u1.lo, v1, &rem_ignored);
// Undo normalization and division of u by 2.
u128_t q0 = {0, q1};
libdivide_u128_shift(&q0.hi, &q0.lo, n);
libdivide_u128_shift(&q0.hi, &q0.lo, -63);
// Make q0 correct or too small by 1
// Equivalent to `if (q0 != 0) q0 = q0 - 1;`
if (q0.hi != 0 || q0.lo != 0)
{
q0.hi -= (q0.lo == 0); // borrow
q0.lo -= 1;
}
// Now q0 is correct.
// Compute q0 * v as q0v
// = (q0.hi << 64 + q0.lo) * (v.hi << 64 + v.lo)
// = (q0.hi * v.hi << 128) + (q0.hi * v.lo << 64) +
// (q0.lo * v.hi << 64) + q0.lo * v.lo)
// Each term is 128 bit
// High half of full product (upper 128 bits!) are dropped
u128_t q0v = {0, 0};
q0v.hi = q0.hi * v.lo + q0.lo * v.hi + libdivide_mullhi_u64(q0.lo, v.lo);
q0v.lo = q0.lo * v.lo;
// Compute u - q0v as u_q0v
// This is the remainder
u128_t u_q0v = u;
u_q0v.hi -= q0v.hi + (u.lo < q0v.lo); // second term is borrow
u_q0v.lo -= q0v.lo;
// Check if u_q0v >= v
// This checks if our remainder is larger than the divisor
if ((u_q0v.hi > v.hi) || (u_q0v.hi == v.hi && u_q0v.lo >= v.lo))
{
// Increment q0
q0.lo += 1;
q0.hi += (q0.lo == 0); // carry
// Subtract v from remainder
u_q0v.hi -= v.hi + (u_q0v.lo < v.lo);
u_q0v.lo -= v.lo;
}
*r_hi = u_q0v.hi;
*r_lo = u_q0v.lo;
LIBDIVIDE_ASSERT(q0.hi == 0);
return q0.lo;
#endif
}
////////// UINT16
static LIBDIVIDE_INLINE struct libdivide_u16_t libdivide_internal_u16_gen(
uint16_t d, int branchfree)
{
if (d == 0)
{
LIBDIVIDE_ERROR("divider must be != 0");
}
struct libdivide_u16_t result;
uint8_t floor_log_2_d = (uint8_t)(15 - libdivide_count_leading_zeros16(d));
// Power of 2
if ((d & (d - 1)) == 0)
{
// We need to subtract 1 from the shift value in case of an unsigned
// branchfree divider because there is a hardcoded right shift by 1
// in its division algorithm. Because of this we also need to add back
// 1 in its recovery algorithm.
result.magic = 0;
result.more = (uint8_t)(floor_log_2_d - (branchfree != 0));
}
else
{
uint8_t more;
uint16_t rem, proposed_m;
proposed_m = libdivide_32_div_16_to_16((uint16_t)1 << floor_log_2_d, 0, d, &rem);
LIBDIVIDE_ASSERT(rem > 0 && rem < d);
const uint16_t e = d - rem;
// This power works if e < 2**floor_log_2_d.
if (!branchfree && (e < ((uint16_t)1 << floor_log_2_d)))
{
// This power works
more = floor_log_2_d;
}
else
{
// We have to use the general 17-bit algorithm. We need to compute
// (2**power) / d. However, we already have (2**(power-1))/d and
// its remainder. By doubling both, and then correcting the
// remainder, we can compute the larger division.
// don't care about overflow here - in fact, we expect it
proposed_m += proposed_m;
const uint16_t twice_rem = rem + rem;
if (twice_rem >= d || twice_rem < rem) proposed_m += 1;
more = floor_log_2_d | LIBDIVIDE_ADD_MARKER;
}
result.magic = 1 + proposed_m;
result.more = more;
// result.more's shift should in general be ceil_log_2_d. But if we
// used the smaller power, we subtract one from the shift because we're
// using the smaller power. If we're using the larger power, we
// subtract one from the shift because it's taken care of by the add
// indicator. So floor_log_2_d happens to be correct in both cases.
}
return result;
}
struct libdivide_u16_t libdivide_u16_gen(uint16_t d)
{
return libdivide_internal_u16_gen(d, 0);
}
struct libdivide_u16_branchfree_t libdivide_u16_branchfree_gen(uint16_t d)
{
if (d == 1)
{
LIBDIVIDE_ERROR("branchfree divider must be != 1");
}
struct libdivide_u16_t tmp = libdivide_internal_u16_gen(d, 1);
struct libdivide_u16_branchfree_t ret =
{
tmp.magic, (uint8_t)(tmp.more & LIBDIVIDE_16_SHIFT_MASK)
};
return ret;
}
// The original libdivide_u16_do takes a const pointer. However, this cannot be used
// with a compile time constant libdivide_u16_t: it will generate a warning about
// taking the address of a temporary. Hence this overload.
uint16_t libdivide_u16_do_raw(uint16_t numer, uint16_t magic, uint8_t more)
{
if (!magic)
{
return numer >> more;
}
else
{
uint16_t q = libdivide_mullhi_u16(magic, numer);
if (more & LIBDIVIDE_ADD_MARKER)
{
uint16_t t = ((numer - q) >> 1) + q;
return t >> (more & LIBDIVIDE_16_SHIFT_MASK);
}
else
{
// All upper bits are 0,
// don't need to mask them off.
return q >> more;
}
}
}
uint16_t libdivide_u16_do(uint16_t numer, const struct libdivide_u16_t *denom)
{
return libdivide_u16_do_raw(numer, denom->magic, denom->more);
}
uint16_t libdivide_u16_branchfree_do(
uint16_t numer, const struct libdivide_u16_branchfree_t *denom)
{
uint16_t q = libdivide_mullhi_u16(denom->magic, numer);
uint16_t t = ((numer - q) >> 1) + q;
return t >> denom->more;
}
uint16_t libdivide_u16_recover(const struct libdivide_u16_t *denom)
{
uint8_t more = denom->more;
uint8_t shift = more & LIBDIVIDE_16_SHIFT_MASK;
if (!denom->magic)
{
return (uint16_t)1 << shift;
}
else if (!(more & LIBDIVIDE_ADD_MARKER))
{
// We compute q = n/d = n*m / 2^(16 + shift)
// Therefore we have d = 2^(16 + shift) / m
// We need to ceil it.
// We know d is not a power of 2, so m is not a power of 2,
// so we can just add 1 to the floor
uint16_t hi_dividend = (uint16_t)1 << shift;
uint16_t rem_ignored;
return 1 + libdivide_32_div_16_to_16(hi_dividend, 0, denom->magic, &rem_ignored);
}
else
{
// Here we wish to compute d = 2^(16+shift+1)/(m+2^16).
// Notice (m + 2^16) is a 17 bit number. Use 32 bit division for now
// Also note that shift may be as high as 15, so shift + 1 will
// overflow. So we have to compute it as 2^(16+shift)/(m+2^16), and
// then double the quotient and remainder.
uint32_t half_n = (uint32_t)1 << (16 + shift);
uint32_t d = ((uint32_t)1 << 16) | denom->magic;
// Note that the quotient is guaranteed <= 16 bits, but the remainder
// may need 17!
uint16_t half_q = (uint16_t)(half_n / d);
uint32_t rem = half_n % d;
// We computed 2^(16+shift)/(m+2^16)
// Need to double it, and then add 1 to the quotient if doubling th
// remainder would increase the quotient.
// Note that rem<<1 cannot overflow, since rem < d and d is 17 bits
uint16_t full_q = half_q + half_q + ((rem << 1) >= d);
// We rounded down in gen (hence +1)
return full_q + 1;
}
}
uint16_t libdivide_u16_branchfree_recover(const struct libdivide_u16_branchfree_t *denom)
{
uint8_t more = denom->more;
uint8_t shift = more & LIBDIVIDE_16_SHIFT_MASK;
if (!denom->magic)
{
return (uint16_t)1 << (shift + 1);
}
else
{
// Here we wish to compute d = 2^(16+shift+1)/(m+2^16).
// Notice (m + 2^16) is a 17 bit number. Use 32 bit division for now
// Also note that shift may be as high as 15, so shift + 1 will
// overflow. So we have to compute it as 2^(16+shift)/(m+2^16), and
// then double the quotient and remainder.
uint32_t half_n = (uint32_t)1 << (16 + shift);
uint32_t d = ((uint32_t)1 << 16) | denom->magic;
// Note that the quotient is guaranteed <= 16 bits, but the remainder
// may need 17!
uint16_t half_q = (uint16_t)(half_n / d);
uint32_t rem = half_n % d;
// We computed 2^(16+shift)/(m+2^16)
// Need to double it, and then add 1 to the quotient if doubling th
// remainder would increase the quotient.
// Note that rem<<1 cannot overflow, since rem < d and d is 33 bits
uint16_t full_q = half_q + half_q + ((rem << 1) >= d);
// We rounded down in gen (hence +1)
return full_q + 1;
}
}
////////// UINT32
static LIBDIVIDE_INLINE struct libdivide_u32_t libdivide_internal_u32_gen(
uint32_t d, int branchfree)
{
if (d == 0)
{
LIBDIVIDE_ERROR("divider must be != 0");
}
struct libdivide_u32_t result;
uint32_t floor_log_2_d = 31 - libdivide_count_leading_zeros32(d);
// Power of 2
if ((d & (d - 1)) == 0)
{
// We need to subtract 1 from the shift value in case of an unsigned
// branchfree divider because there is a hardcoded right shift by 1
// in its division algorithm. Because of this we also need to add back
// 1 in its recovery algorithm.
result.magic = 0;
result.more = (uint8_t)(floor_log_2_d - (branchfree != 0));
}
else
{
uint8_t more;
uint32_t rem, proposed_m;
proposed_m = libdivide_64_div_32_to_32((uint32_t)1 << floor_log_2_d, 0, d, &rem);
LIBDIVIDE_ASSERT(rem > 0 && rem < d);
const uint32_t e = d - rem;
// This power works if e < 2**floor_log_2_d.
if (!branchfree && (e < ((uint32_t)1 << floor_log_2_d)))
{
// This power works
more = (uint8_t)floor_log_2_d;
}
else
{
// We have to use the general 33-bit algorithm. We need to compute
// (2**power) / d. However, we already have (2**(power-1))/d and
// its remainder. By doubling both, and then correcting the
// remainder, we can compute the larger division.
// don't care about overflow here - in fact, we expect it
proposed_m += proposed_m;
const uint32_t twice_rem = rem + rem;
if (twice_rem >= d || twice_rem < rem) proposed_m += 1;
more = (uint8_t)(floor_log_2_d | LIBDIVIDE_ADD_MARKER);
}
result.magic = 1 + proposed_m;
result.more = more;
// result.more's shift should in general be ceil_log_2_d. But if we
// used the smaller power, we subtract one from the shift because we're
// using the smaller power. If we're using the larger power, we
// subtract one from the shift because it's taken care of by the add
// indicator. So floor_log_2_d happens to be correct in both cases.
}
return result;
}
struct libdivide_u32_t libdivide_u32_gen(uint32_t d)
{
return libdivide_internal_u32_gen(d, 0);
}
struct libdivide_u32_branchfree_t libdivide_u32_branchfree_gen(uint32_t d)
{
if (d == 1)
{
LIBDIVIDE_ERROR("branchfree divider must be != 1");
}
struct libdivide_u32_t tmp = libdivide_internal_u32_gen(d, 1);
struct libdivide_u32_branchfree_t ret =
{
tmp.magic, (uint8_t)(tmp.more & LIBDIVIDE_32_SHIFT_MASK)
};
return ret;
}
uint32_t libdivide_u32_do(uint32_t numer, const struct libdivide_u32_t *denom)
{
uint8_t more = denom->more;
if (!denom->magic)