diff options
Diffstat (limited to 'src/runtime/rand.go')
| -rw-r--r-- | src/runtime/rand.go | 47 |
1 files changed, 36 insertions, 11 deletions
diff --git a/src/runtime/rand.go b/src/runtime/rand.go index a30845b585..353e0e0f42 100644 --- a/src/runtime/rand.go +++ b/src/runtime/rand.go @@ -192,7 +192,8 @@ func mrandinit(mp *m) { } bootstrapRandReseed() // erase key we just extracted mp.chacha8.Init64(seed) - mp.cheaprand = rand() + mp.cheaprand = uint32(rand()) + mp.cheaprand64 = rand() } // randn is like rand() % n but faster. @@ -227,14 +228,12 @@ func randn(n uint32) uint32 { func cheaprand() uint32 { mp := getg().m // Implement wyrand: https://github.com/wangyi-fudan/wyhash - // Only the platform that bits.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.cheaprand += 0xa0761d6478bd642f - hi, lo := bits.Mul64(mp.cheaprand, mp.cheaprand^0xe7037ed1a0b428db) - return uint32(hi ^ lo) + // Only the platform that supports 64-bit multiplication + // natively should be allowed. + if bits.UintSize == 64 { + mp.cheaprand += 0x53c5ca59 + hi, lo := bits.Mul32(mp.cheaprand, mp.cheaprand^0x74743c1b) + return hi ^ lo } // Implement xorshift64+: 2 32-bit xorshift sequences added together. @@ -242,7 +241,7 @@ func cheaprand() uint32 { // 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.cheaprand)) + t := (*[2]uint32)(unsafe.Pointer(&mp.cheaprand64)) s1, s0 := t[0], t[1] s1 ^= s1 << 17 s1 = s1 ^ s0 ^ s1>>7 ^ s0>>16 @@ -269,7 +268,33 @@ func cheaprand() uint32 { //go:linkname cheaprand64 //go:nosplit func cheaprand64() int64 { - return int64(cheaprand())<<31 ^ int64(cheaprand()) + return int64(cheaprandu64() & ^(uint64(1) << 63)) +} + +// cheaprandu64 is a non-cryptographic-quality 64-bit random generator +// suitable for calling at very high frequency (such as during sampling decisions). +// it is "cheap" in the sense of both expense and quality. +// +// cheaprandu64 must not be exported to other packages: +// the rule is that other packages using runtime-provided +// randomness must always use rand. +// +//go:nosplit +func cheaprandu64() uint64 { + // Implement wyrand: https://github.com/wangyi-fudan/wyhash + // Only the platform that bits.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 := getg().m + // Implement wyrand: https://github.com/wangyi-fudan/wyhash + mp.cheaprand64 += 0xa0761d6478bd642f + hi, lo := bits.Mul64(mp.cheaprand64, mp.cheaprand64^0xe7037ed1a0b428db) + return hi ^ lo + } + + return uint64(cheaprand())<<32 | uint64(cheaprand()) } // cheaprandn is like cheaprand() % n but faster. |