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runtime: use better hash for floating point inputs

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Hashing on the bytes instead of the words does
a (much) better job of using all the bits, so that
maps of floats have linear performance.

LGTM=khr
R=golang-codereviews, khr
CC=adonovan, golang-codereviews
https://golang.org/cl/126720044
This commit is contained in:
Russ Cox 2014-08-06 16:47:54 -04:00
parent 1338f327b2
commit 5fbcdb2661
1 changed files with 2 additions and 5 deletions
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7
src/pkg/runtime/alg.go
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@ -75,7 +75,7 @@ func f32hash(a *float32, s, h uintptr) uintptr {
case f != f: case f != f:
return c1 * (c0 ^ h ^ uintptr(fastrand2())) // any kind of NaN return c1 * (c0 ^ h ^ uintptr(fastrand2())) // any kind of NaN
default: default:
return c1 * (c0 ^ h ^ uintptr(*(*uint32)(unsafe.Pointer(a)))) return memhash(unsafe.Pointer(a), 4, h)
} }
} }
@ -86,11 +86,8 @@ func f64hash(a *float64, s, h uintptr) uintptr {
return c1 * (c0 ^ h) // +0, -0 return c1 * (c0 ^ h) // +0, -0
case f != f: case f != f:
return c1 * (c0 ^ h ^ uintptr(fastrand2())) // any kind of NaN return c1 * (c0 ^ h ^ uintptr(fastrand2())) // any kind of NaN
case ptrSize == 4:
x := (*[2]uintptr)(unsafe.Pointer(a))
return c1 * (c0 ^ h ^ (x[1] * c1) ^ x[0])
default: default:
return c1 * (c0 ^ h ^ *(*uintptr)(unsafe.Pointer(a))) return memhash(unsafe.Pointer(a), 8, h)
} }
} }