lib/bytes: implement function ParseHexDump

The ParseHexDump parse the default output of [hexdump](1) utility from
parameter in back into stream of byte.

An example of default output of hexdump is

	0000000 7865 5f70 6964 2f72 0000 0000 0000 0000
	0000010 0000 0000 0000 0000 0000 0000 0000 0000
	*
	0000060 0000 0000 3030 3030 3537 0035 3030 3130

The first column is the address and the rest of the column is the data.
Each data column is 16-bit words in big-endian order, so in the above
example, the first byte would be 65, second byte is 78 and so on.
The asterisk "*" means that the address from 0000020 to 0000050 is equal to
the previous line, 0000010.

[hexdump]: https://man.archlinux.org/man/hexdump.1

1 files changed, 93 insertions, 0 deletions

diff --git a/lib/bytes/bytes.go b/lib/bytes/bytes.go
index 8656b4a9..d3e1022a 100644
--- a/lib/bytes/bytes.go
+++ b/lib/bytes/bytes.go
@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"strconv"
 	"unicode"
 
 	inbytes "github.com/shuLhan/share/internal/bytes"
@@ -295,6 +296,98 @@ func MergeSpaces(in []byte) (out []byte) {
 	return out
 }
 
+// ParseHexDump parse the default output of [hexdump](1) utility from
+// parameter in back into stream of byte.
+//
+// An example of default output of hexdump is
+//
+//	0000000 7865 5f70 6964 2f72 0000 0000 0000 0000
+//	0000010 0000 0000 0000 0000 0000 0000 0000 0000
+//	*
+//	0000060 0000 0000 3030 3030 3537 0035 3030 3130
+//
+// The first column is the address and the rest of the column is the data.
+// Each data column is 16-bit words in big-endian order, so in the above
+// example, the first byte would be 65, second byte is 78 and so on.
+// The asterisk "*" means that the address from 0000020 to 0000050 is equal to
+// the previous line, 0000010.
+//
+// [hexdump]: https://man.archlinux.org/man/hexdump.1
+func ParseHexDump(in []byte) (out []byte, err error) {
+	var (
+		logp        = `ParseHexDump`
+		parser      = NewParser(in, []byte(" \n"))
+		d      byte = 255 // Just to make the first for-loop pass.
+
+		token      []byte
+		vint64     int64
+		x          int
+		isAsterisk bool
+	)
+	for d != 0 {
+		// Read the address.
+		token, d = parser.Read()
+		if len(token) == 0 {
+			break
+		}
+		if len(token) == 1 {
+			if token[0] != '*' {
+				break
+			}
+			isAsterisk = true
+			continue
+		}
+
+		vint64, err = strconv.ParseInt(string(token), 16, 64)
+		if err != nil {
+			return nil, fmt.Errorf(`%s: %w`, logp, err)
+		}
+
+		if isAsterisk {
+			if len(out) > 0 {
+				var start = len(out)
+				if start < 16 {
+					start = 0
+				} else {
+					start = start - 16
+				}
+				var (
+					prevRow      = out[start:]
+					identicalRow = int((vint64 - int64(len(out))) / 16)
+				)
+				for x = 0; x < identicalRow; x++ {
+					out = append(out, prevRow...)
+				}
+			}
+		}
+
+		// Read the two-hex, 16-bit words.
+		for x = 0; x < 8; x++ {
+			token, d = parser.Read()
+			if len(token) == 0 {
+				break
+			}
+
+			vint64, err = strconv.ParseInt(string(token), 16, 64)
+			if err != nil {
+				return nil, fmt.Errorf(`%s: %w`, logp, err)
+			}
+
+			out = append(out, byte(vint64))
+			out = append(out, byte(vint64>>8))
+
+			if d == '\n' {
+				break
+			}
+		}
+		// Ignore trailing characters.
+		if d != '\n' {
+			parser.SkipLine()
+		}
+	}
+	return out, nil
+}
+
 // PrintHex will print each byte in slice as hexadecimal value into N column
 // length.
 func PrintHex(title string, data []byte, col int) {