Normalizes a float32 LE raw file

normalize-f32le.go

//
// Normalizes a float32 little-endian raw file to the first few averaged values.
// The averaged values will be treated as the baseline and all values in the
// file will be relative to that.
//
// 2020.11.04  darell tan
//

package main

import (
	"fmt"
	"io"
	"math"
	"os"
)

var avgSamples = 10 // number of values to average

func readFloat(buf []byte) float32 {
	v := uint32(buf[0]) << 0
	v |= uint32(buf[1]) << 8
	v |= uint32(buf[2]) << 16
	v |= uint32(buf[3]) << 24
	return math.Float32frombits(v)
}

func writeFloat(buf []byte, v float32) {
	v2 := math.Float32bits(v)
	buf[0] = byte(v2 >> 0)
	buf[1] = byte(v2 >> 8)
	buf[2] = byte(v2 >> 16)
	buf[3] = byte(v2 >> 24)
}

func main() {
	fname := os.Args[1]

	f, err := os.OpenFile(fname, os.O_RDWR, 0644)
	if err != nil {
		panic(err)
	}
	defer f.Close()

	buf := make([]byte, 1024*4)

	// read samples for averaging
	if _, err = f.Read(buf[:4*avgSamples]); err != nil {
		panic(err)
	}

	normValueSum := float64(0)
	for i := 0; i < avgSamples; i++ {
		v := readFloat(buf[i*4 : i*4+4])
		normValueSum += float64(v)
	}
	normValue := float32(normValueSum / float64(avgSamples))
	fmt.Printf("normal value: %f\n", normValue)

	f.Seek(0, 0) // restart

	for offset := uint64(0); ; {
		n, err := f.Read(buf)
		if err == io.EOF {
			break
		}
		if err != nil {
			panic(err)
		}

		for i := 0; i < n; i += 4 {
			v := readFloat(buf[i : i+4])
			v -= normValue
			writeFloat(buf[i:], v)
		}

		f.Seek(int64(offset), 0)
		f.Write(buf)

		offset += uint64(n)
	}
}