1 package runtime
2 3 // This file implements various core algorithms used in the runtime package and
4 // standard library.
5 6 import (
7 "unsafe"
8 )
9 10 // This function is needed by math/rand since Go 1.20.
11 // See: https://github.com/golang/go/issues/54880
12 //
13 //go:linkname rand_fastrand64 math/rand.fastrand64
14 func rand_fastrand64() uint64 {
15 return fastrand64()
16 }
17 18 // This function is used by hash/maphash.
19 // This function isn't required anymore since Go 1.22, so should be removed once
20 // that becomes the minimum requirement.
21 func fastrand() uint32 {
22 xorshift32State = xorshift32(xorshift32State)
23 return xorshift32State
24 }
25 26 func initRand() {
27 r, _ := hardwareRand()
28 xorshift64State = uint64(r | 1) // protect against 0
29 xorshift32State = uint32(xorshift64State)
30 }
31 32 var xorshift32State uint32 = 1
33 34 func xorshift32(x uint32) uint32 {
35 // Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs".
36 // Improved sequence based on
37 // http://www.iro.umontreal.ca/~lecuyer/myftp/papers/xorshift.pdf
38 x ^= x << 7
39 x ^= x >> 1
40 x ^= x << 9
41 return x
42 }
43 44 // This function is used by hash/maphash.
45 // This function isn't required anymore since Go 1.22, so should be removed once
46 // that becomes the minimum requirement.
47 func fastrand64() uint64 {
48 xorshift64State = xorshiftMult64(xorshift64State)
49 return xorshift64State
50 }
51 52 var xorshift64State uint64 = 1
53 54 // 64-bit xorshift multiply rng from http://vigna.di.unimi.it/ftp/papers/xorshift.pdf
55 func xorshiftMult64(x uint64) uint64 {
56 x ^= x >> 12 // a
57 x ^= x << 25 // b
58 x ^= x >> 27 // c
59 return x * 2685821657736338717
60 }
61 62 // This function is used by hash/maphash.
63 func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
64 if unsafe.Sizeof(uintptr(0)) > 4 {
65 return uintptr(hash64(p, s, seed))
66 }
67 return uintptr(hash32(p, s, seed))
68 }
69 70 // Function that's called from various packages starting with Go 1.22.
71 func rand() uint64 {
72 // Return a random number from hardware, falling back to software if
73 // unavailable.
74 n, ok := hardwareRand()
75 if !ok {
76 // Fallback to static random number.
77 // Not great, but we can't do much better than this.
78 n = fastrand64()
79 }
80 return n
81 }
82