1 files changed, 53 insertions, 0 deletions
diff --git a/modules/brotli/enc/prefix.h b/modules/brotli/enc/prefix.h
new file mode 100644
index 000000000..fd359a478
--- /dev/null
+++ b/modules/brotli/enc/prefix.h
@@ -0,0 +1,53 @@
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* Functions for encoding of integers into prefix codes the amount of extra
+   bits, and the actual values of the extra bits. */
+
+#ifndef BROTLI_ENC_PREFIX_H_
+#define BROTLI_ENC_PREFIX_H_
+
+#include "../common/constants.h"
+#include "../common/platform.h"
+#include <brotli/types.h>
+#include "./fast_log.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+/* Here distance_code is an intermediate code, i.e. one of the special codes or
+   the actual distance increased by BROTLI_NUM_DISTANCE_SHORT_CODES - 1. */
+static BROTLI_INLINE void PrefixEncodeCopyDistance(size_t distance_code,
+                                                   size_t num_direct_codes,
+                                                   size_t postfix_bits,
+                                                   uint16_t* code,
+                                                   uint32_t* extra_bits) {
+  if (distance_code < BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes) {
+    *code = (uint16_t)distance_code;
+    *extra_bits = 0;
+    return;
+  } else {
+    size_t dist = ((size_t)1 << (postfix_bits + 2u)) +
+        (distance_code - BROTLI_NUM_DISTANCE_SHORT_CODES - num_direct_codes);
+    size_t bucket = Log2FloorNonZero(dist) - 1;
+    size_t postfix_mask = (1u << postfix_bits) - 1;
+    size_t postfix = dist & postfix_mask;
+    size_t prefix = (dist >> bucket) & 1;
+    size_t offset = (2 + prefix) << bucket;
+    size_t nbits = bucket - postfix_bits;
+    *code = (uint16_t)((nbits << 10) |
+        (BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes +
+         ((2 * (nbits - 1) + prefix) << postfix_bits) + postfix));
+    *extra_bits = (uint32_t)((dist - offset) >> postfix_bits);
+  }
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}  /* extern "C" */
+#endif
+
+#endif  /* BROTLI_ENC_PREFIX_H_ */