From 9b4075c8811e0acb1339a52b3c122f23d2da2c32 Mon Sep 17 00:00:00 2001
From: Jordan Orelli <jordanorelli@gmail.com>
Date: Mon, 1 Aug 2016 12:43:02 -0400
Subject: [PATCH] gonna need this bit twiddling thing

---
 bit.go      | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 bit_test.go | 37 +++++++++++++++++++++++++++++++++++++
 parser.go   |  2 ++
 3 files changed, 90 insertions(+)
 create mode 100644 bit.go
 create mode 100644 bit_test.go

diff --git a/bit.go b/bit.go
new file mode 100644
index 0000000..15532b6
--- /dev/null
+++ b/bit.go
@@ -0,0 +1,51 @@
+package main
+
+import (
+	"io"
+)
+
+// a bitBuffer is a buffer of raw data that is not necessarily byte-aligned,
+// for performing bitwise reads and manipulation. The bulk of this source is
+// adapted from the bitReader defined in the standard library bzip2 package.
+type bitBuffer struct {
+	source  []byte // the source data to be read. This slice is never modified
+	index   int    // position of the last byte read out of source
+	scratch uint64 // scratch register of bits worthy of manipulation
+	bits    uint   // bit width of the scratch register
+	err     error  // stored error
+}
+
+func newBitBuffer(buf []byte) *bitBuffer {
+	return &bitBuffer{source: buf}
+}
+
+func (b *bitBuffer) readBits(bits uint) uint64 {
+	for bits > b.bits {
+		if b.index >= len(b.source) {
+			b.err = io.ErrUnexpectedEOF
+			return 0
+		}
+		b.scratch <<= 8
+		b.scratch |= uint64(b.source[b.index])
+		b.index += 1
+		b.bits += 8
+	}
+
+	// b.scratch looks like this (assuming that b.bits = 14 and bits = 6):
+	// Bit: 111111
+	//      5432109876543210
+	//
+	//         (6 bits, the desired output)
+	//        |-----|
+	//        V     V
+	//      0101101101001110
+	//        ^            ^
+	//        |------------|
+	//           b.bits (num valid bits)
+	//
+	// This the next line right shifts the desired bits into the
+	// least-significant places and masks off anything above.
+	n := (b.scratch >> (b.bits - bits)) & ((1 << bits) - 1)
+	b.bits -= bits
+	return n
+}
diff --git a/bit_test.go b/bit_test.go
new file mode 100644
index 0000000..79d7a4f
--- /dev/null
+++ b/bit_test.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"io"
+	"testing"
+)
+
+func TestBits(t *testing.T) {
+	buf := []byte{0x00}
+	bb := newBitBuffer(buf)
+	for i := 0; i < 8; i++ {
+		if bb.readBits(1) != 0x00 {
+			t.Error("hahha what")
+		}
+		if bb.err != nil {
+			t.Errorf("oh weird error: %v", bb.err)
+		}
+	}
+	if bb.readBits(1) != 0x00 {
+		t.Error("hahha what")
+	}
+	if bb.err != io.ErrUnexpectedEOF {
+		t.Errorf("oh weird error: %v", bb.err)
+	}
+
+	buf = []byte{0x10}
+	bb = newBitBuffer(buf)
+	if n := bb.readBits(4); n != 0x01 {
+		t.Errorf("shit. wanted %v, got %v", 0x01, n)
+	}
+	if n := bb.readBits(4); n != 0x00 {
+		t.Errorf("poop. wanted %v, got %v", 0x00, n)
+	}
+	if bb.err != nil {
+		t.Errorf("fuck")
+	}
+}
diff --git a/parser.go b/parser.go
index ac5c30f..9039435 100644
--- a/parser.go
+++ b/parser.go
@@ -154,8 +154,10 @@ func (p *parser) readMessage() (*message, error) {
 		if _, err := io.ReadFull(p.source, buf); err != nil {
 			return nil, wrap(err, "readMessage couldn't read message body")
 		}
+		// TODO: pool these!
 		return &message{cmd, int64(tick), compressed, buf}, nil
 	}
 
+	// TODO: pool these!
 	return &message{cmd, int64(tick), compressed, nil}, nil
 }