enc/b64.go: flesh it out

1 files changed, 31 insertions, 0 deletions

diff --git a/enc/b64.go b/enc/b64.go
index e69de29..0ea0a4c 100644
--- a/enc/b64.go
+++ b/enc/b64.go
@@ -0,0 +1,31 @@
+package enc
+
+const b64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+
+func HexToBase64(hex string) string {
+	hb := []byte(hex)
+
+	b64 := ""
+	for i := 0; i <= len(hb)-3; i = i + 3 {
+		a := fromHexChar(hb[i])<<8 | fromHexChar(hb[i+1])<<4 | fromHexChar(hb[i+2])
+		b64 += encode(a >> 6)
+		b64 += encode(a & 0b111111)
+	}
+	return b64
+}
+
+func encode(b uint16) string {
+	return string(b64_table[b])
+}
+
+// adapted from
+// https://go.googlesource.com/go/+/refs/tags/go1.15/src/encoding/hex/hex.go#83
+func fromHexChar(c byte) uint16 {
+	switch {
+	case '0' <= c && c <= '9':
+		return uint16(c - '0')
+	case 'a' <= c && c <= 'f':
+		return uint16(c - 'a' + 10)
+	}
+	return 0
+}