diff options
Diffstat (limited to 'dependencies/pkg/mod/github.com/cespare/xxhash/v2@v2.1.2/xxhash_unsafe.go')
-rw-r--r-- | dependencies/pkg/mod/github.com/cespare/xxhash/v2@v2.1.2/xxhash_unsafe.go | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/github.com/cespare/xxhash/v2@v2.1.2/xxhash_unsafe.go b/dependencies/pkg/mod/github.com/cespare/xxhash/v2@v2.1.2/xxhash_unsafe.go new file mode 100644 index 0000000..376e0ca --- /dev/null +++ b/dependencies/pkg/mod/github.com/cespare/xxhash/v2@v2.1.2/xxhash_unsafe.go @@ -0,0 +1,57 @@ +// +build !appengine + +// This file encapsulates usage of unsafe. +// xxhash_safe.go contains the safe implementations. + +package xxhash + +import ( + "unsafe" +) + +// In the future it's possible that compiler optimizations will make these +// XxxString functions unnecessary by realizing that calls such as +// Sum64([]byte(s)) don't need to copy s. See https://golang.org/issue/2205. +// If that happens, even if we keep these functions they can be replaced with +// the trivial safe code. + +// NOTE: The usual way of doing an unsafe string-to-[]byte conversion is: +// +// var b []byte +// bh := (*reflect.SliceHeader)(unsafe.Pointer(&b)) +// bh.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data +// bh.Len = len(s) +// bh.Cap = len(s) +// +// Unfortunately, as of Go 1.15.3 the inliner's cost model assigns a high enough +// weight to this sequence of expressions that any function that uses it will +// not be inlined. Instead, the functions below use a different unsafe +// conversion designed to minimize the inliner weight and allow both to be +// inlined. There is also a test (TestInlining) which verifies that these are +// inlined. +// +// See https://github.com/golang/go/issues/42739 for discussion. + +// Sum64String computes the 64-bit xxHash digest of s. +// It may be faster than Sum64([]byte(s)) by avoiding a copy. +func Sum64String(s string) uint64 { + b := *(*[]byte)(unsafe.Pointer(&sliceHeader{s, len(s)})) + return Sum64(b) +} + +// WriteString adds more data to d. It always returns len(s), nil. +// It may be faster than Write([]byte(s)) by avoiding a copy. +func (d *Digest) WriteString(s string) (n int, err error) { + d.Write(*(*[]byte)(unsafe.Pointer(&sliceHeader{s, len(s)}))) + // d.Write always returns len(s), nil. + // Ignoring the return output and returning these fixed values buys a + // savings of 6 in the inliner's cost model. + return len(s), nil +} + +// sliceHeader is similar to reflect.SliceHeader, but it assumes that the layout +// of the first two words is the same as the layout of a string. +type sliceHeader struct { + s string + cap int +} |