From 78401edeb890f54d579a654aeba41bb4edd21203 Mon Sep 17 00:00:00 2001
From: Markus Walther <mark@saiko.tech>
Date: Tue, 7 Dec 2021 22:03:12 +0000
Subject: [PATCH] implement Bsp.CRC32() - aka CRC_MapFile()

---
 .gitattributes |  1 +
 crc.go         | 38 ++++++++++++++++++++++++++++++++++++++
 crc_test.go    | 37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 .gitattributes
 create mode 100644 crc.go
 create mode 100644 crc_test.go

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..bf70ec9
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+*.bsp.gz filter=lfs diff=lfs merge=lfs -text
diff --git a/crc.go b/crc.go
new file mode 100644
index 0000000..7a1fb95
--- /dev/null
+++ b/crc.go
@@ -0,0 +1,38 @@
+package bsp
+
+import (
+	"hash/crc32"
+	"sort"
+)
+
+func (bsp *Bsp) CRC32() (uint32, error) {
+	const lumpCount = 64
+
+	crc := crc32.NewIEEE()
+
+	lumpList := make([]LumpId, lumpCount)
+	for i := 0; i < lumpCount; i++ {
+		lumpList[i] = LumpId(i)
+	}
+
+	sort.Slice(lumpList, func(i, j int) bool {
+		return bsp.header.Lumps[lumpList[i]].Offset < bsp.header.Lumps[lumpList[j]].Offset
+	})
+
+	for i := 0; i < lumpCount; i++ {
+		l := lumpList[i]
+		if l == LumpEntities {
+			continue
+		}
+
+		_, err := crc.Write(bsp.RawLump(l).raw)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	// see CRC32_Final
+	res := crc.Sum32() ^ 0xFFFFFFFF
+
+	return res, nil
+}
diff --git a/crc_test.go b/crc_test.go
new file mode 100644
index 0000000..fa31181
--- /dev/null
+++ b/crc_test.go
@@ -0,0 +1,37 @@
+package bsp_test
+
+import (
+	"compress/gzip"
+	"os"
+	"testing"
+
+	"github.com/galaco/bsp"
+)
+
+func TestBsp_Crc(t *testing.T) {
+	f, err := os.Open("ar_baggage.bsp.gz")
+	if err != nil {
+		t.Error(err)
+	}
+
+	gzR, err := gzip.NewReader(f)
+	if err != nil {
+		t.Error(err)
+	}
+
+	bspF, err := bsp.ReadFromStream(gzR)
+	if err != nil {
+		t.Error(err)
+	}
+
+	res, err := bspF.CRC32()
+	if err != nil {
+		t.Error("unexpected error:", err)
+	}
+
+	const expected = 2836609078
+
+	if res != expected {
+		t.Errorf("CRC incorrect, expected %d got %d", expected, res)
+	}
+}