// Copyright 2014 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.

package runtime

import _ "unsafe"

//go:linkname fastrand C.rand
func fastrand() uint32

/* TODO(xsw):
func fastrand() uint32 {
	mp := getg().m
	// Implement wyrand: https://github.com/wangyi-fudan/wyhash
	// Only the platform that math.Mul64 can be lowered
	// by the compiler should be in this list.
	if goarch.IsAmd64|goarch.IsArm64|goarch.IsPpc64|
		goarch.IsPpc64le|goarch.IsMips64|goarch.IsMips64le|
		goarch.IsS390x|goarch.IsRiscv64|goarch.IsLoong64 == 1 {
		mp.fastrand += 0xa0761d6478bd642f
		hi, lo := math.Mul64(mp.fastrand, mp.fastrand^0xe7037ed1a0b428db)
		return uint32(hi ^ lo)
	}

	// Implement xorshift64+: 2 32-bit xorshift sequences added together.
	// Shift triplet [17,7,16] was calculated as indicated in Marsaglia's
	// Xorshift paper: https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf
	// This generator passes the SmallCrush suite, part of TestU01 framework:
	// http://simul.iro.umontreal.ca/testu01/tu01.html
	t := (*[2]uint32)(unsafe.Pointer(&mp.fastrand))
	s1, s0 := t[0], t[1]
	s1 ^= s1 << 17
	s1 = s1 ^ s0 ^ s1>>7 ^ s0>>16
	t[0], t[1] = s0, s1
	return s0 + s1
}
*/

const (
	// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
	_64bit       = 1 << (^uintptr(0) >> 63) / 2
	heapAddrBits = (_64bit)*48 + (1-_64bit)*(32)
	maxAlloc     = (1 << heapAddrBits) - (1-_64bit)*1
)
