init

src/core/fastlz.h

@@ -0,0 +1,60 @@
+#pragma once
+// FastLZ (level 1 and 2) block decompressor, as used by Noita for chunk files and stream info.
+// The level is in the top 3 bits of the first byte (0 = level 1, 1 = level 2).
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+namespace ng {
+
+// Returns false on malformed input or if the output would exceed max_out.
+inline bool fastlz_decompress(const uint8_t* in, size_t in_len, std::vector<uint8_t>& out, size_t max_out) {
+    out.clear();
+    if (in_len == 0) return true;
+    const int level = (in[0] >> 5) + 1;
+    if (level != 1 && level != 2) return false;
+    size_t ip = 0;
+    uint32_t ctrl = in[ip++] & 31;
+    for (;;) {
+        if (ctrl >= 32) {
+            uint32_t len = (ctrl >> 5) - 1;
+            uint32_t ofs = (ctrl & 31) << 8;
+            if (len == 6) {
+                uint8_t code;
+                do {
+                    if (ip >= in_len) return false;
+                    code = in[ip++];
+                    len += code;
+                } while (code == 255 && level == 2);
+                if (level == 1 && false) return false;
+            }
+            if (ip >= in_len) return false;
+            const uint8_t code = in[ip++];
+            ofs += code;
+            size_t back;
+            if (level == 2 && code == 255 && (ctrl & 31) == 31) {
+                if (ip + 1 >= in_len) return false;
+                ofs = ((uint32_t)in[ip] << 8) + in[ip + 1];
+                ip += 2;
+                back = (size_t)ofs + 8191 + 1; // 16-bit distance: MAX_L2_DISTANCE + 1 (the +1 is easy to miss)
+            } else {
+                back = (size_t)ofs + 1;
+            }
+            if (back > out.size()) return false;
+            len += 3;
+            if (out.size() + len > max_out) return false;
+            size_t ref = out.size() - back;
+            for (uint32_t k = 0; k < len; ++k) out.push_back(out[ref + k]);
+        } else {
+            const size_t n = (size_t)ctrl + 1;
+            if (ip + n > in_len || out.size() + n > max_out) return false;
+            out.insert(out.end(), in + ip, in + ip + n);
+            ip += n;
+        }
+        if (ip >= in_len) break;
+        ctrl = in[ip++];
+    }
+    return true;
+}
+
+} // namespace ng