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internal/bloom/murmur.go

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+// Copyright 2013, Sébastien Paolacci. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package murmur3 provides an amd64 native (Go generic fallback)
+// implementation of the murmur3 hash algorithm for strings and slices.
+//
+// Assembly is provided for amd64 go1.5+; pull requests are welcome for other
+// architectures.
+package bloom
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+type bmixer interface {
+	bmix(p []byte) (tail []byte)
+	Size() (n int)
+	reset()
+}
+
+type digest struct {
+	clen int      // Digested input cumulative length.
+	tail []byte   // 0 to Size()-1 bytes view of `buf'.
+	buf  [16]byte // Expected (but not required) to be Size() large.
+	bmixer
+}
+
+func (d *digest) BlockSize() int { return 1 }
+
+func (d *digest) Write(p []byte) (n int, err error) {
+	n = len(p)
+	d.clen += n
+
+	if len(d.tail) > 0 {
+		// Stick back pending bytes.
+		nfree := d.Size() - len(d.tail) // nfree ∈ [1, d.Size()-1].
+		if nfree < len(p) {
+			// One full block can be formed.
+			block := append(d.tail, p[:nfree]...)
+			p = p[nfree:]
+			_ = d.bmix(block) // No tail.
+		} else {
+			// Tail's buf is large enough to prevent reallocs.
+			p = append(d.tail, p...)
+		}
+	}
+
+	d.tail = d.bmix(p)
+
+	// Keep own copy of the 0 to Size()-1 pending bytes.
+	nn := copy(d.buf[:], d.tail)
+	d.tail = d.buf[:nn]
+
+	return n, nil
+}
+
+func (d *digest) Reset() {
+	d.clen = 0
+	d.tail = nil
+	d.bmixer.reset()
+}
+
+func strslice(slice []byte) string {
+	var str string
+	slicehdr := ((*reflect.SliceHeader)(unsafe.Pointer(&slice)))
+	strhdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
+	strhdr.Data = slicehdr.Data
+	strhdr.Len = slicehdr.Len
+	return str
+}