// Copyright 2023 The rust-ggstd authors. All rights reserved.
// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

use super::bits_tables;

// //go:generate go run make_tables.go

// const uintSize = 32 << (^uint(0) >> 63) // 32 or 64

// // UintSize is the size of a uint in bits.
// const UintSize = uintSize

// // --- LeadingZeros ---

// // LeadingZeros returns the number of leading zero bits in x; the result is UintSize for x == 0.
// fn LeadingZeros(x uint) int { return UintSize - Len(x) }

// // LeadingZeros8 returns the number of leading zero bits in x; the result is 8 for x == 0.
// fn LeadingZeros8(x u8) int { return 8 - Len8(x) }

// // LeadingZeros16 returns the number of leading zero bits in x; the result is 16 for x == 0.
// fn LeadingZeros16(x u16) int { return 16 - Len16(x) }

// // LeadingZeros32 returns the number of leading zero bits in x; the result is 32 for x == 0.
// fn LeadingZeros32(x uint32) int { return 32 - Len32(x) }

// // LeadingZeros64 returns the number of leading zero bits in x; the result is 64 for x == 0.
// fn LeadingZeros64(x uint64) int { return 64 - Len64(x) }

// // --- TrailingZeros ---

// // See http://supertech.csail.mit.edu/papers/debruijn.pdf
// const deBruijn32 = 0x077CB531

// var deBruijn32tab = [32]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,
// }

// const deBruijn64 = 0x03f79d71b4ca8b09

// var deBruijn64tab = [64]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,
// }

// // TrailingZeros returns the number of trailing zero bits in x; the result is UintSize for x == 0.
// fn TrailingZeros(x uint) int {
// 	if UintSize == 32 {
// 		return TrailingZeros32(uint32(x))
// 	}
// 	return TrailingZeros64(uint64(x))
// }

// // TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0.
// fn TrailingZeros8(x u8) int {
// 	return int(ntz8tab[x])
// }

// // TrailingZeros16 returns the number of trailing zero bits in x; the result is 16 for x == 0.
// fn TrailingZeros16(x u16) int {
// 	if x == 0 {
// 		return 16
// 	}
// 	// see comment in TrailingZeros64
// 	return int(deBruijn32tab[uint32(x&-x)*deBruijn32>>(32-5)])
// }

// // TrailingZeros32 returns the number of trailing zero bits in x; the result is 32 for x == 0.
// fn TrailingZeros32(x uint32) int {
// 	if x == 0 {
// 		return 32
// 	}
// 	// see comment in TrailingZeros64
// 	return int(deBruijn32tab[(x&-x)*deBruijn32>>(32-5)])
// }

// // TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
// fn TrailingZeros64(x uint64) 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(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)])
// }

// // --- OnesCount ---

// const m0 = 0x5555555555555555 // 01010101 ...
// const m1 = 0x3333333333333333 // 00110011 ...
// const m2 = 0x0f0f0f0f0f0f0f0f // 00001111 ...
// const m3 = 0x00ff00ff00ff00ff // etc.
// const m4 = 0x0000ffff0000ffff

// // OnesCount returns the number of one bits ("population count") in x.
// fn OnesCount(x uint) int {
// 	if UintSize == 32 {
// 		return OnesCount32(uint32(x))
// 	}
// 	return OnesCount64(uint64(x))
// }

// // OnesCount8 returns the number of one bits ("population count") in x.
// fn OnesCount8(x u8) int {
// 	return int(pop8tab[x])
// }

// // OnesCount16 returns the number of one bits ("population count") in x.
// fn OnesCount16(x u16) int {
// 	return int(pop8tab[x>>8] + pop8tab[x&0xff])
// }

// // OnesCount32 returns the number of one bits ("population count") in x.
// fn OnesCount32(x uint32) int {
// 	return int(pop8tab[x>>24] + pop8tab[x>>16&0xff] + pop8tab[x>>8&0xff] + pop8tab[x&0xff])
// }

// // OnesCount64 returns the number of one bits ("population count") in x.
// fn OnesCount64(x uint64) 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.
// 	const m = 1<<64 - 1
// 	x = x>>1&(m0&m) + x&(m0&m)
// 	x = x>>2&(m1&m) + x&(m1&m)
// 	x = (x>>4 + x) & (m2 & m)
// 	x += x >> 8
// 	x += x >> 16
// 	x += x >> 32
// 	return int(x) & (1<<7 - 1)
// }

// // --- RotateLeft ---

// // RotateLeft returns the value of x rotated left by (k mod UintSize) bits.
// // To rotate x right by k bits, call RotateLeft(x, -k).
// //
// // This function's execution time does not depend on the inputs.
// fn RotateLeft(x uint, k int) uint {
// 	if UintSize == 32 {
// 		return uint(rotate_left32(uint32(x), k))
// 	}
// 	return uint(RotateLeft64(uint64(x), k))
// }

// // RotateLeft8 returns the value of x rotated left by (k mod 8) bits.
// // To rotate x right by k bits, call RotateLeft8(x, -k).
// //
// // This function's execution time does not depend on the inputs.
// fn RotateLeft8(x u8, k int) u8 {
// 	const n = 8
// 	s := uint(k) & (n - 1)
// 	return x<<s | x>>(n-s)
// }

// // RotateLeft16 returns the value of x rotated left by (k mod 16) bits.
// // To rotate x right by k bits, call RotateLeft16(x, -k).
// //
// // This function's execution time does not depend on the inputs.
// fn RotateLeft16(x u16, k int) -> u16 {
// 	const n = 16
// 	s := uint(k) & (n - 1)
// 	return x<<s | x>>(n-s)
// }

/// rotate_left32 returns the value of x rotated left by (k mod 32) bits.
/// To rotate x right by k bits, call rotate_left32(x, -k).
///
/// This function's execution time does not depend on the inputs.
pub fn rotate_left32(x: u32, k: isize) -> u32 {
    if k % 32 == 0 {
        return x;
    }
    let n = 32;
    let s = (k as usize) & (n - 1);
    x << s | x >> (n - s)
}

// // RotateLeft64 returns the value of x rotated left by (k mod 64) bits.
// // To rotate x right by k bits, call RotateLeft64(x, -k).
// //
// // This function's execution time does not depend on the inputs.
// fn RotateLeft64(x uint64, k int) uint64 {
// 	const n = 64
// 	s := uint(k) & (n - 1)
// 	return x<<s | x>>(n-s)
// }

// // --- Reverse ---

// // Reverse returns the value of x with its bits in reversed order.
// fn Reverse(x uint) uint {
// 	if UintSize == 32 {
// 		return uint(Reverse32(uint32(x)))
// 	}
// 	return uint(Reverse64(uint64(x)))
// }

// reverse8 returns the value of x with its bits in reversed order.
pub fn reverse8(x: u8) -> u8 {
    bits_tables::REV8TAB[x as usize]
}

// reverse16 returns the value of x with its bits in reversed order.
pub fn reverse16(x: u16) -> u16 {
    ((bits_tables::REV8TAB[(x >> 8) as usize]) as u16)
        | ((bits_tables::REV8TAB[(x & 0xff) as usize]) as u16) << 8
}

// // Reverse32 returns the value of x with its bits in reversed order.
// fn Reverse32(x uint32) uint32 {
// 	const m = 1<<32 - 1
// 	x = x>>1&(m0&m) | x&(m0&m)<<1
// 	x = x>>2&(m1&m) | x&(m1&m)<<2
// 	x = x>>4&(m2&m) | x&(m2&m)<<4
// 	return ReverseBytes32(x)
// }

// // Reverse64 returns the value of x with its bits in reversed order.
// fn Reverse64(x uint64) uint64 {
// 	const m = 1<<64 - 1
// 	x = x>>1&(m0&m) | x&(m0&m)<<1
// 	x = x>>2&(m1&m) | x&(m1&m)<<2
// 	x = x>>4&(m2&m) | x&(m2&m)<<4
// 	return ReverseBytes64(x)
// }

// // --- ReverseBytes ---

// // ReverseBytes returns the value of x with its bytes in reversed order.
// //
// // This function's execution time does not depend on the inputs.
// fn ReverseBytes(x uint) uint {
// 	if UintSize == 32 {
// 		return uint(ReverseBytes32(uint32(x)))
// 	}
// 	return uint(ReverseBytes64(uint64(x)))
// }

// // ReverseBytes16 returns the value of x with its bytes in reversed order.
// //
// // This function's execution time does not depend on the inputs.
// fn ReverseBytes16(x u16) -> u16 {
// 	return x>>8 | x<<8
// }

// // ReverseBytes32 returns the value of x with its bytes in reversed order.
// //
// // This function's execution time does not depend on the inputs.
// fn ReverseBytes32(x uint32) uint32 {
// 	const m = 1<<32 - 1
// 	x = x>>8&(m3&m) | x&(m3&m)<<8
// 	return x>>16 | x<<16
// }

// // ReverseBytes64 returns the value of x with its bytes in reversed order.
// //
// // This function's execution time does not depend on the inputs.
// fn ReverseBytes64(x uint64) uint64 {
// 	const m = 1<<64 - 1
// 	x = x>>8&(m3&m) | x&(m3&m)<<8
// 	x = x>>16&(m4&m) | x&(m4&m)<<16
// 	return x>>32 | x<<32
// }

// // --- Len ---

// // Len returns the minimum number of bits required to represent x; the result is 0 for x == 0.
// fn Len(x uint) int {
// 	if UintSize == 32 {
// 		return Len32(uint32(x))
// 	}
// 	return Len64(uint64(x))
// }

// // Len8 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
// fn Len8(x u8) int {
// 	return int(len8tab[x])
// }

// // Len16 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
// fn Len16(x u16) (n int) {
// 	if x >= 1<<8 {
// 		x >>= 8
// 		n = 8
// 	}
// 	return n + int(len8tab[x])
// }

// // Len32 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
// fn Len32(x uint32) (n int) {
// 	if x >= 1<<16 {
// 		x >>= 16
// 		n = 16
// 	}
// 	if x >= 1<<8 {
// 		x >>= 8
// 		n += 8
// 	}
// 	return n + int(len8tab[x])
// }

// // Len64 returns the minimum number of bits required to represent x; the result is 0 for x == 0.
// fn Len64(x uint64) (n int) {
// 	if x >= 1<<32 {
// 		x >>= 32
// 		n = 32
// 	}
// 	if x >= 1<<16 {
// 		x >>= 16
// 		n += 16
// 	}
// 	if x >= 1<<8 {
// 		x >>= 8
// 		n += 8
// 	}
// 	return n + int(len8tab[x])
// }

// // --- 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.
// //
// // This function's execution time does not depend on the inputs.
// fn Add(x, y, carry uint) (sum, carryOut uint) {
// 	if UintSize == 32 {
// 		s32, c32 := Add32(uint32(x), uint32(y), uint32(carry))
// 		return uint(s32), uint(c32)
// 	}
// 	s64, c64 := Add64(uint64(x), uint64(y), uint64(carry))
// 	return uint(s64), uint(c64)
// }

// // Add32 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 Add32(x, y, carry uint32) (sum, carryOut uint32) {
// 	sum64 := uint64(x) + uint64(y) + uint64(carry)
// 	sum = uint32(sum64)
// 	carryOut = uint32(sum64 >> 32)
// 	return
// }

// // Add64 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 Add64(x, y, carry uint64) (sum, carryOut uint64) {
// 	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).
// 	carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
// 	return
// }

// // --- 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.
// //
// // This function's execution time does not depend on the inputs.
// fn Sub(x, y, borrow uint) (diff, borrowOut uint) {
// 	if UintSize == 32 {
// 		d32, b32 := Sub32(uint32(x), uint32(y), uint32(borrow))
// 		return uint(d32), uint(b32)
// 	}
// 	d64, b64 := Sub64(uint64(x), uint64(y), uint64(borrow))
// 	return uint(d64), uint(b64)
// }

// // Sub32 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 Sub32(x, y, borrow uint32) (diff, borrowOut uint32) {
// 	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).
// 	borrowOut = ((^x & y) | (^(x ^ y) & diff)) >> 31
// 	return
// }

// // Sub64 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 Sub64(x, y, borrow uint64) (diff, borrowOut uint64) {
// 	diff = x - y - borrow
// 	// See Sub32 for the bit logic.
// 	borrowOut = ((^x & y) | (^(x ^ y) & diff)) >> 63
// 	return
// }

// // --- Full-width multiply ---

// // Mul returns the full-width 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(x, y uint) (hi, lo uint) {
// 	if UintSize == 32 {
// 		h, l := Mul32(uint32(x), uint32(y))
// 		return uint(h), uint(l)
// 	}
// 	h, l := Mul64(uint64(x), uint64(y))
// 	return uint(h), uint(l)
// }

// // Mul32 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 Mul32(x, y uint32) (hi, lo uint32) {
// 	tmp := uint64(x) * uint64(y)
// 	hi, lo = uint32(tmp>>32), uint32(tmp)
// 	return
// }

// // Mul64 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 Mul64(x, y uint64) (hi, lo uint64) {
// 	const mask32 = 1<<32 - 1
// 	x0 := x & mask32
// 	x1 := x >> 32
// 	y0 := y & mask32
// 	y1 := y >> 32
// 	w0 := x0 * y0
// 	t := x1*y0 + w0>>32
// 	w1 := t & mask32
// 	w2 := t >> 32
// 	w1 += x0 * y1
// 	hi = x1*y1 + w2 + w1>>32
// 	lo = x * y
// 	return
// }

// // --- Full-width divide ---

// // Div 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 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
// fn Div(hi, lo, y uint) (quo, rem uint) {
// 	if UintSize == 32 {
// 		q, r := Div32(uint32(hi), uint32(lo), uint32(y))
// 		return uint(q), uint(r)
// 	}
// 	q, r := Div64(uint64(hi), uint64(lo), uint64(y))
// 	return uint(q), uint(r)
// }

// // Div32 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.
// // Div32 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
// fn Div32(hi, lo, y uint32) (quo, rem uint32) {
// 	if y != 0 && y <= hi {
// 		panic(overflowError)
// 	}
// 	z := uint64(hi)<<32 | uint64(lo)
// 	quo, rem = uint32(z/uint64(y)), uint32(z%uint64(y))
// 	return
// }

// // Div64 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.
// // Div64 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
// fn Div64(hi, lo, y uint64) (quo, rem uint64) {
// 	if y == 0 {
// 		panic(divideError)
// 	}
// 	if y <= hi {
// 		panic(overflowError)
// 	}

// 	// If high part is zero, we can directly return the results.
// 	if hi == 0 {
// 		return lo / y, lo % y
// 	}

// 	s := uint(LeadingZeros64(y))
// 	y <<= s

// 	const (
// 		two32  = 1 << 32
// 		mask32 = two32 - 1
// 	)
// 	yn1 := y >> 32
// 	yn0 := y & mask32
// 	un32 := hi<<s | lo>>(64-s)
// 	un10 := lo << s
// 	un1 := un10 >> 32
// 	un0 := un10 & mask32
// 	q1 := un32 / yn1
// 	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
// 	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 returns the remainder of (hi, lo) divided by y. Rem panics for
// // y == 0 (division by zero) but, unlike Div, it doesn't panic on a
// // quotient overflow.
// fn Rem(hi, lo, y uint) uint {
// 	if UintSize == 32 {
// 		return uint(Rem32(uint32(hi), uint32(lo), uint32(y)))
// 	}
// 	return uint(Rem64(uint64(hi), uint64(lo), uint64(y)))
// }

// // Rem32 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 Rem32(hi, lo, y uint32) uint32 {
// 	return uint32((uint64(hi)<<32 | uint64(lo)) % uint64(y))
// }

// // Rem64 returns the remainder of (hi, lo) divided by y. Rem64 panics
// // for y == 0 (division by zero) but, unlike Div64, it doesn't panic
// // on a quotient overflow.
// fn Rem64(hi, lo, y uint64) uint64 {
// 	// We scale down hi so that hi < y, then use Div64 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 := Div64(hi%y, lo, y)
// 	return rem
// }

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn test_rotate_left() {
        assert_eq!(
            0b_00000000_00000000_00000000_00001111,
            rotate_left32(0b1111, 0)
        );
        assert_eq!(
            0b_00000000_00000000_00000000_00001111,
            rotate_left32(0b1111, 32)
        );
        assert_eq!(
            0b_00000000_00000000_00000000_00001111,
            rotate_left32(0b1111, -32)
        );
        assert_eq!(
            0b_00000000_00000000_00000000_00011110,
            rotate_left32(0b1111, 1)
        );
        assert_eq!(
            0b_10000000_00000000_00000000_00000111,
            rotate_left32(0b1111, -1)
        );
        assert_eq!(
            0b_00000000_00000000_00000000_00111100,
            rotate_left32(0b1111, 2)
        );
        assert_eq!(
            0b_11000000_00000000_00000000_00000011,
            rotate_left32(0b1111, -2)
        );
        assert_eq!(
            0b_00000000_00000000_00000000_00011110,
            rotate_left32(0b1111, 33)
        );
        assert_eq!(
            0b_10000000_00000000_00000000_00000111,
            rotate_left32(0b1111, -33)
        );
    }
}