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vendor/github.com/andybalholm/brotli/prefix.go

@@ -0,0 +1,30 @@
+package brotli
+
+/* 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. */
+
+/* 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. */
+func prefixEncodeCopyDistance(distance_code uint, num_direct_codes uint, postfix_bits uint, code *uint16, extra_bits *uint32) {
+	if distance_code < numDistanceShortCodes+num_direct_codes {
+		*code = uint16(distance_code)
+		*extra_bits = 0
+		return
+	} else {
+		var dist uint = (uint(1) << (postfix_bits + 2)) + (distance_code - numDistanceShortCodes - num_direct_codes)
+		var bucket uint = uint(log2FloorNonZero(dist) - 1)
+		var postfix_mask uint = (1 << postfix_bits) - 1
+		var postfix uint = dist & postfix_mask
+		var prefix uint = (dist >> bucket) & 1
+		var offset uint = (2 + prefix) << bucket
+		var nbits uint = bucket - postfix_bits
+		*code = uint16(nbits<<10 | (numDistanceShortCodes + num_direct_codes + ((2*(nbits-1) + prefix) << postfix_bits) + postfix))
+		*extra_bits = uint32((dist - offset) >> postfix_bits)
+	}
+}