From 4a09f5844cb1649ecbdfec260628285cfcd640ec Mon Sep 17 00:00:00 2001
From: BiSaXa <1669855+BiSaXa@users.noreply.github.com>
Date: Sun, 4 Sep 2022 01:07:28 +0300
Subject: init - first full version

---
 bitreader.go | 129 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 bitreader.go

(limited to 'bitreader.go')

diff --git a/bitreader.go b/bitreader.go
new file mode 100644
index 0000000..9d9a273
--- /dev/null
+++ b/bitreader.go
@@ -0,0 +1,129 @@
+package main
+
+import (
+	"fmt"
+	"math/bits"
+	"strconv"
+	"strings"
+)
+
+type ReaderType struct {
+	data  []byte
+	base  int
+	index int
+	lsb   bool
+}
+
+func Reader(data []byte) *ReaderType {
+	return &ReaderType{
+		data:  data,
+		base:  0,
+		index: 0,
+		lsb:   false,
+	}
+}
+
+func ReaderLSB(data []byte) *ReaderType {
+	dataReversed := data
+	for index, byteValue := range data {
+		dataReversed[index] = bits.Reverse8(byteValue)
+	}
+	return &ReaderType{
+		data:  dataReversed,
+		base:  0,
+		index: 0,
+		lsb:   true,
+	}
+}
+
+func (reader *ReaderType) SkipBits(bits int) error {
+	if bits <= 0 {
+		return fmt.Errorf("SkipBits Error: Bits value %d lower or equals than 0.", bits)
+	}
+	for reader.index+bits > 7 {
+		reader.base++
+		reader.index = 0
+		bits -= 8
+	}
+	reader.index += bits
+	return nil
+}
+
+func (reader *ReaderType) ReadBits32(bits int) (int, error) {
+	if bits <= 0 {
+		return -1, fmt.Errorf("ReadBits Error: Bits value %d lower or equals than 0.", bits)
+	}
+	if bits > 32 {
+		return -1, fmt.Errorf("ReadBits Error: Bits value %d higher than 32.", bits)
+	}
+	err := reader.checkAvailableBits(bits)
+	if err != nil {
+		return -1, err
+	}
+	if reader.lsb {
+		var output string
+		// Go to last bit and read backwards from there
+		reader.base += bits / 8
+		reader.index += bits % 8
+		if reader.index > 7 {
+			reader.index -= 8
+			reader.base++
+		}
+		for i := 0; i < bits; i++ {
+			reader.index--
+			if reader.index < 0 {
+				reader.base--
+				reader.index = 7
+			}
+			binary := fmt.Sprintf("%08b", reader.data[reader.base])
+			binaryArr := strings.Split(binary, "")
+			output += binaryArr[reader.index]
+		}
+		// Return to last bit after reading
+		reader.base += bits / 8
+		reader.index += bits % 8
+		if reader.index > 7 {
+			reader.index -= 8
+		}
+		// Conversion of string binary to int
+		value, err := strconv.ParseUint(output, 2, 32)
+		if err != nil {
+			return -1, fmt.Errorf("%s", err)
+		}
+		return int(value), nil
+	} else {
+		var output string
+		for i := 0; i < bits; i++ {
+			binary := fmt.Sprintf("%08b", reader.data[reader.base])
+			binaryArr := strings.Split(binary, "")
+			output += binaryArr[reader.index]
+			reader.index++
+			if reader.index > 7 {
+				reader.base++
+				reader.index = 0
+			}
+		}
+		// Conversion of string binary to int
+		value, err := strconv.ParseUint(output, 2, 32)
+		if err != nil {
+			return -1, fmt.Errorf("%s", err)
+		}
+		return int(value), nil
+	}
+}
+
+func (reader *ReaderType) ReadBit() (bool, error) {
+	value, err := reader.ReadBits32(1)
+	if err != nil {
+		return false, fmt.Errorf("ReadBit Error: %s", err)
+	}
+	return value != 0, nil
+}
+
+func (reader *ReaderType) checkAvailableBits(bits int) error {
+	availableBits := (len(reader.data)-reader.base)*8 - reader.index
+	if availableBits < bits {
+		return fmt.Errorf("BitReaderOutOfBounds: Wanted to read %d bit(s) but only %d bit(s) is/are available.", bits, availableBits)
+	}
+	return nil
+}
-- 
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