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v/vlib/math/bits/bits.v
2020-02-12 11:32:03 +01:00

496 lines
15 KiB
V

// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module bits
const (
// See http://supertech.csail.mit.edu/papers/debruijn.pdf
de_bruijn32 = u32(0x077CB531)
de_bruijn32tab = [byte(0), 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9,
]
de_bruijn64 = (0x03f79d71b4ca8b09)
de_bruijn64tab = [byte(0), 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
]
)
const (
m0 = 0x5555555555555555 // 01010101 ...
m1 = 0x3333333333333333 // 00110011 ...
m2 = 0x0f0f0f0f0f0f0f0f // 00001111 ...
m3 = 0x00ff00ff00ff00ff // etc.
m4 = 0x0000ffff0000ffff
)
const (
// save importing math mod just for these
max_u32 = 4294967295
max_u64 = 18446744073709551615
)
// --- LeadingZeros ---
// leading_zeros_8 returns the number of leading zero bits in x; the result is 8 for x == 0.
pub fn leading_zeros_8(x byte) int {
return 8 - len_8(x)
}
// leading_zeros_16 returns the number of leading zero bits in x; the result is 16 for x == 0.
pub fn leading_zeros_16(x u16) int {
return 16 - len_16(x)
}
// leading_zeros_32 returns the number of leading zero bits in x; the result is 32 for x == 0.
pub fn leading_zeros_32(x u32) int {
return 32 - len_32(x)
}
// leading_zeros_64 returns the number of leading zero bits in x; the result is 64 for x == 0.
pub fn leading_zeros_64(x u64) int {
return 64 - len_64(x)
}
// --- TrailingZeros ---
// trailing_zeros_8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
pub fn trailing_zeros_8(x byte) int {
return int(ntz_8_tab[x])
}
// trailing_zeros_16 returns the number of trailing zero bits in x; the result is 16 for x == 0.
pub fn trailing_zeros_16(x u16) int {
if x == 0 {
return 16
}
// see comment in trailing_zeros_64
return int(de_bruijn32tab[u32(x & -x) * de_bruijn32>>(32 - 5)])
}
// trailing_zeros_32 returns the number of trailing zero bits in x; the result is 32 for x == 0.
pub fn trailing_zeros_32(x u32) int {
if x == 0 {
return 32
}
// see comment in trailing_zeros_64
return int(de_bruijn32tab[(x & -x) * de_bruijn32>>(32 - 5)])
}
// trailing_zeros_64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
pub fn trailing_zeros_64(x u64) int {
if x == 0 {
return 64
}
// If popcount is fast, replace code below with return popcount(^x & (x - 1)).
//
// x & -x leaves only the right-most bit set in the word. Let k be the
// index of that bit. Since only a single bit is set, the value is two
// to the power of k. Multiplying by a power of two is equivalent to
// left shifting, in this case by k bits. The de Bruijn (64 bit) constant
// is such that all six bit, consecutive substrings are distinct.
// Therefore, if we have a left shifted version of this constant we can
// find by how many bits it was shifted by looking at which six bit
// substring ended up at the top of the word.
// (Knuth, volume 4, section 7.3.1)
return int(de_bruijn64tab[(x & -x) * de_bruijn64>>(64 - 6)])
}
// --- OnesCount ---
// ones_count_8 returns the number of one bits ("population count") in x.
pub fn ones_count_8(x byte) int {
return int(pop_8_tab[x])
}
// ones_count_16 returns the number of one bits ("population count") in x.
pub fn ones_count_16(x u16) int {
return int(pop_8_tab[x>>8] + pop_8_tab[x & u16(0xff)])
}
// ones_count_32 returns the number of one bits ("population count") in x.
pub fn ones_count_32(x u32) int {
return int(pop_8_tab[x>>24] + pop_8_tab[x>>16 & 0xff] + pop_8_tab[x>>8 & 0xff] + pop_8_tab[x & u32(0xff)])
}
// ones_count_64 returns the number of one bits ("population count") in x.
pub fn ones_count_64(x u64) int {
// Implementation: Parallel summing of adjacent bits.
// See "Hacker's Delight", Chap. 5: Counting Bits.
// The following pattern shows the general approach:
//
// x = x>>1&(m0&m) + x&(m0&m)
// x = x>>2&(m1&m) + x&(m1&m)
// x = x>>4&(m2&m) + x&(m2&m)
// x = x>>8&(m3&m) + x&(m3&m)
// x = x>>16&(m4&m) + x&(m4&m)
// x = x>>32&(m5&m) + x&(m5&m)
// return int(x)
//
// Masking (& operations) can be left away when there's no
// danger that a field's sum will carry over into the next
// field: Since the result cannot be > 64, 8 bits is enough
// and we can ignore the masks for the shifts by 8 and up.
// Per "Hacker's Delight", the first line can be simplified
// more, but it saves at best one instruction, so we leave
// it alone for clarity.
mut y := (x>>u64(1) & (m0 & max_u64)) + (x & (m0 & max_u64))
y = (y>>u64(2) & (m1 & max_u64)) + (y & (m1 & max_u64))
y = ((y>>4) + y) & (m2 & max_u64)
y += y>>8
y += y>>16
y += y>>32
return int(y) & ((1<<7) - 1)
}
// --- RotateLeft ---
// rotate_left_8 returns the value of x rotated left by (k mod 8) bits.
// To rotate x right by k bits, call rotate_left_8(x, -k).
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn rotate_left_8(x byte, k int) byte {
n := byte(8)
s := byte(k) & (n - byte(1))
return ((x<<s) | (x>>(n - s)))
}
// rotate_left_16 returns the value of x rotated left by (k mod 16) bits.
// To rotate x right by k bits, call rotate_left_16(x, -k).
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn rotate_left_16(x u16, k int) u16 {
n := u16(16)
s := u16(k) & (n - u16(1))
return ((x<<s) | (x>>(n - s)))
}
// rotate_left_32 returns the value of x rotated left by (k mod 32) bits.
// To rotate x right by k bits, call rotate_left_32(x, -k).
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn rotate_left_32(x u32, k int) u32 {
n := u32(32)
s := u32(k) & (n - u32(1))
return ((x<<s) | (x>>(n - s)))
}
// rotate_left_64 returns the value of x rotated left by (k mod 64) bits.
// To rotate x right by k bits, call rotate_left_64(x, -k).
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn rotate_left_64(x u64, k int) u64 {
n := u64(64)
s := u64(k) & (n - u64(1))
return ((x<<s) | (x>>(n - s)))
}
// --- Reverse ---
// reverse_8 returns the value of x with its bits in reversed order.
[inline]
pub fn reverse_8(x byte) byte {
return rev_8_tab[x]
}
// reverse_16 returns the value of x with its bits in reversed order.
[inline]
pub fn reverse_16(x u16) u16 {
return u16(rev_8_tab[x>>8]) | (u16(rev_8_tab[x & u16(0xff)])<<8)
}
// reverse_32 returns the value of x with its bits in reversed order.
[inline]
pub fn reverse_32(x u32) u32 {
mut y := (x>>u32(1) & (m0 & max_u32) | ((x & (m0 & max_u32))<<1))
y = (y>>u32(2) & (m1 & max_u32) | ((y & (m1 & max_u32))<<u32(2)))
y = (y>>u32(4) & (m2 & max_u32) | ((y & (m2 & max_u32))<<u32(4)))
return reverse_bytes_32(y)
}
// reverse_64 returns the value of x with its bits in reversed order.
[inline]
pub fn reverse_64(x u64) u64 {
mut y := (x>>u64(1) & (m0 & max_u64) | ((x & (m0 & max_u64))<<1))
y = (y>>u64(2) & (m1 & max_u64) | ((y & (m1 & max_u64))<<2))
y = (y>>u64(4) & (m2 & max_u64) | ((y & (m2 & max_u64))<<4))
return reverse_bytes_64(y)
}
// --- ReverseBytes ---
// reverse_bytes_16 returns the value of x with its bytes in reversed order.
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn reverse_bytes_16(x u16) u16 {
return (x>>8) | (x<<8)
}
// reverse_bytes_32 returns the value of x with its bytes in reversed order.
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn reverse_bytes_32(x u32) u32 {
y := (x>>u32(8) & (m3 & max_u32) | ((x & (m3 & max_u32))<<u32(8)))
return (y>>16) | (y<<16)
}
// reverse_bytes_64 returns the value of x with its bytes in reversed order.
//
// This function's execution time does not depend on the inputs.
[inline]
pub fn reverse_bytes_64(x u64) u64 {
mut y := (x>>u64(8) & (m3 & max_u64) | ((x & (m3 & max_u64))<<u64(8)))
y = (y>>u64(16) & (m4 & max_u64) | ((y & (m4 & max_u64))<<u64(16)))
return (y>>32) | (y<<32)
}
// --- Len ---
// len_8 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
pub fn len_8(x byte) int {
return int(len_8_tab[x])
}
// len_16 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
pub fn len_16(x u16) int {
mut y := x
mut n := 0
if y >= 1<<8 {
y >>= 8
n = 8
}
return n + int(len_8_tab[y])
}
// len_32 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
pub fn len_32(x u32) int {
mut y := x
mut n := 0
if y >= 1<<16 {
y >>= 16
n = 16
}
if y >= 1<<8 {
y >>= 8
n += 8
}
return n + int(len_8_tab[y])
}
// len_64 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
pub fn len_64(x u64) int {
mut y := x
mut n := 0
if y >= u64(1)<<u64(32) {
y >>= 32
n = 32
}
if y >= u64(1)<<u64(16) {
y >>= 16
n += 16
}
if y >= u64(1)<<u64(8) {
y >>= 8
n += 8
}
return n + int(len_8_tab[y])
}
// --- Add with carry ---
// Add returns the sum with carry of x, y and carry: sum = x + y + carry.
// The carry input must be 0 or 1; otherwise the behavior is undefined.
// The carryOut output is guaranteed to be 0 or 1.
//
// add_32 returns the sum with carry of x, y and carry: sum = x + y + carry.
// The carry input must be 0 or 1; otherwise the behavior is undefined.
// The carryOut output is guaranteed to be 0 or 1.
//
// This function's execution time does not depend on the inputs.
fn add_32(x u32, y u32, carry u32) (u32, u32) {
sum64 := u64(x) + u64(y) + u64(carry)
sum := u32(sum64)
carry_out := u32(sum64>>32)
return sum, carry_out
}
// add_64 returns the sum with carry of x, y and carry: sum = x + y + carry.
// The carry input must be 0 or 1; otherwise the behavior is undefined.
// The carryOut output is guaranteed to be 0 or 1.
//
// This function's execution time does not depend on the inputs.
fn add_64(x u64, y u64, carry u64) (u64, u64) {
sum := x + y + carry
// The sum will overflow if both top bits are set (x & y) or if one of them
// is (x | y), and a carry from the lower place happened. If such a carry
// happens, the top bit will be 1 + 0 + 1 = 0 (&^ sum).
carry_out := ((x & y) | ((x | y) & ~sum ))>>63
return sum, carry_out
}
// --- Subtract with borrow ---
// Sub returns the difference of x, y and borrow: diff = x - y - borrow.
// The borrow input must be 0 or 1; otherwise the behavior is undefined.
// The borrowOut output is guaranteed to be 0 or 1.
//
// sub_32 returns the difference of x, y and borrow, diff = x - y - borrow.
// The borrow input must be 0 or 1; otherwise the behavior is undefined.
// The borrowOut output is guaranteed to be 0 or 1.
//
// This function's execution time does not depend on the inputs.
fn sub_32(x u32, y u32, borrow u32) (u32, u32) {
diff := x - y - borrow
// The difference will underflow if the top bit of x is not set and the top
// bit of y is set (^x & y) or if they are the same (^(x ^ y)) and a borrow
// from the lower place happens. If that borrow happens, the result will be
// 1 - 1 - 1 = 0 - 0 - 1 = 1 (& diff).
borrow_out := ((~x & y) | (~(x ^ y) & diff))>>31
return diff, borrow_out
}
// sub_64 returns the difference of x, y and borrow: diff = x - y - borrow.
// The borrow input must be 0 or 1; otherwise the behavior is undefined.
// The borrowOut output is guaranteed to be 0 or 1.
//
// This function's execution time does not depend on the inputs.
fn sub_64(x u64, y u64, borrow u64) (u64, u64) {
diff := x - y - borrow
// See Sub32 for the bit logic.
borrow_out := ((~x & y) | (~(x ^ y) & diff))>>63
return diff, borrow_out
}
// --- Full-width multiply ---
const (
two32 = u64(0x1_0000_0000)
mask32 = two32 - 1
overflow_error = "Overflow Error"
divide_error = "Divide Error"
)
// mul_32 returns the 64-bit product of x and y: (hi, lo) = x * y
// with the product bits' upper half returned in hi and the lower
// half returned in lo.
//
// This function's execution time does not depend on the inputs.
fn mul_32(x u32, y u32) (u32, u32) {
tmp := u64(x) * u64(y)
hi := u32(tmp>>32)
lo := u32(tmp)
return hi, lo
}
// mul_64 returns the 128-bit product of x and y: (hi, lo) = x * y
// with the product bits' upper half returned in hi and the lower
// half returned in lo.
//
// This function's execution time does not depend on the inputs.
fn mul_64(x u64, y u64) (u64, u64) {
x0 := x & mask32
x1 := x>>32
y0 := y & mask32
y1 := y>>32
w0 := x0 * y0
t := x1*y0 + (w0>>32)
mut w1 := t & mask32
w2 := t>>32
w1 += x0 * y1
hi := x1*y1 + w2 + (w1>>32)
lo := x * y
return hi, lo
}
// --- Full-width divide ---
// div_32 returns the quotient and remainder of (hi, lo) divided by y:
// quo = (hi, lo)/y, rem = (hi, lo)%y with the dividend bits' upper
// half in parameter hi and the lower half in parameter lo.
// div_32 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
fn div_32(hi u32, lo u32, y u32) (u32, u32) {
if y != 0 && y <= hi {
panic(overflow_error)
}
z := (u64(hi)<<32) | u64(lo)
quo := u32(z/u64(y))
rem := u32(z%u64(y))
return quo, rem
}
// div_64 returns the quotient and remainder of (hi, lo) divided by y:
// quo = (hi, lo)/y, rem = (hi, lo)%y with the dividend bits' upper
// half in parameter hi and the lower half in parameter lo.
// div_64 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
fn div_64(hi u64, lo u64, y1 u64) (u64, u64) {
mut y := y1
if y == 0 {
panic(overflow_error)
}
if y <= hi {
panic(overflow_error)
}
s := u32(leading_zeros_64(y))
y <<= s
yn1 := y>>32
yn0 := y & mask32
un32 := (hi<<s) | (lo>>(64-s))
un10 := lo<<s
un1 := un10>>32
un0 := un10 & mask32
mut q1 := un32 / yn1
mut rhat := un32 - q1*yn1
for q1 >= two32 || q1*yn0 > two32*rhat+un1 {
q1--
rhat += yn1
if rhat >= two32 {
break
}
}
un21 := un32*two32 + un1 - q1*y
mut q0 := un21 / yn1
rhat = un21 - q0*yn1
for q0 >= two32 || q0*yn0 > two32*rhat+un0 {
q0--
rhat += yn1
if rhat >= two32 {
break
}
}
return q1*two32 + q0, (un21*two32 + un0 - q0*y)>>s
}
// rem_32 returns the remainder of (hi, lo) divided by y. Rem32 panics
// for y == 0 (division by zero) but, unlike Div32, it doesn't panic
// on a quotient overflow.
fn rem_32(hi u32, lo u32, y u32) u32 {
return u32((u64(hi)<<32 | u64(lo)) % u64(y))
}
// rem_64 returns the remainder of (hi, lo) divided by y. Rem64 panics
// for y == 0 (division by zero) but, unlike div_64, it doesn't panic
// on a quotient overflow.
fn rem_64(hi, lo, y u64) u64 {
// We scale down hi so that hi < y, then use div_64 to compute the
// rem with the guarantee that it won't panic on quotient overflow.
// Given that
// hi ≡ hi%y (mod y)
// we have
// hi<<64 + lo ≡ (hi%y)<<64 + lo (mod y)
_, rem := div_64(hi%y, lo, y)
return rem
}