go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/common/data/cmpbin/float.go (about)

     1  // Copyright 2015 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package cmpbin
    16  
    17  import (
    18  	"encoding/binary"
    19  	"io"
    20  	"math"
    21  )
    22  
    23  // WriteFloat64 writes a memcmp-sortable float to buf. It returns the number
    24  // of bytes written (8, unless an error occurs), and any write error
    25  // encountered.
    26  func WriteFloat64(buf io.Writer, v float64) (n int, err error) {
    27  	bits := math.Float64bits(v)
    28  	bits = bits ^ (-(bits >> 63) | (1 << 63))
    29  	data := make([]byte, 8)
    30  	binary.BigEndian.PutUint64(data, bits)
    31  	return buf.Write(data)
    32  }
    33  
    34  // ReadFloat64 reads a memcmp-sortable float from buf (as written by
    35  // WriteFloat64). It also returns the number of bytes read (8, unless an error
    36  // occurs), and any read error encountered.
    37  func ReadFloat64(buf io.Reader) (ret float64, n int, err error) {
    38  	// byte-ordered floats http://stereopsis.com/radix.html
    39  	data := make([]byte, 8)
    40  	if n, err = buf.Read(data); err != nil {
    41  		return
    42  	}
    43  	bits := binary.BigEndian.Uint64(data)
    44  	ret = math.Float64frombits(bits ^ (((bits >> 63) - 1) | (1 << 63)))
    45  	return
    46  }