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+// Copyright (C) 2018 Joel Rosdahl
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program; if not, write to the Free Software Foundation, Inc., 51
+// Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+#ifndef HASH_H
+#define HASH_H
+
+#include "system.h"
+
+struct hash;
+
+// Create a new hash.
+struct hash *hash_init(void);
+
+// Create a new hash from an existing hash state.
+struct hash *hash_copy(struct hash *hash);
+
+// Free a hash created by hash_init or hash_copy.
+void hash_free(struct hash *hash);
+
+// Enable debug logging of hashed input to a binary and a text file.
+void hash_enable_debug(
+	struct hash *hash, const char *section_name, FILE *debug_binary,
+	FILE *debug_text);
+
+// Return how many bytes have been hashed.
+size_t hash_input_size(struct hash *hash);
+
+// Return the hash result as a hex string. Caller frees.
+char *hash_result(struct hash *hash);
+
+// Return the hash result as 16 binary bytes.
+void hash_result_as_bytes(struct hash *hash, unsigned char *out);
+
+// Return whether hash1 and hash2 are equal.
+bool hash_equal(struct hash *hash1, struct hash *hash2);
+
+// Hash some data that is unlikely to occur in the input. The idea is twofold:
+//
+// - Delimit things like arguments from each other (e.g., so that -I -O2 and
+//   -I-O2 hash differently).
+// - Tag different types of hashed information so that it's possible to do
+//   conditional hashing of information in a safe way (e.g., if we want to hash
+//   information X if CCACHE_A is set and information Y if CCACHE_B is set,
+//   there should never be a hash collision risk).
+void hash_delimiter(struct hash *hash, const char *type);
+
+// Hash bytes in a buffer.
+//
+// If hash debugging is enabled, the bytes are written verbatim to the text
+// input file.
+void hash_buffer(struct hash *hash, const void *s, size_t len);
+
+// Hash a string.
+//
+// If hash debugging is enabled, the string is written to the text input file
+// followed by a newline.
+void hash_string(struct hash *hash, const char *s);
+
+// Hash a string with a known size.
+//
+// If hash debugging is enabled, the string is written to the text input file
+// followed by a newline.
+void hash_string_buffer(struct hash *hash, const char *s, int length);
+
+// Hash an integer.
+//
+// If hash debugging is enabled, the integer is written in text form to the
+// text input file followed by a newline.
+void hash_int(struct hash *hash, int x);
+
+// Add contents of an open file to the hash.
+//
+// If hash debugging is enabled, the data is written verbatim to the text input
+// file.
+//
+// Returns true on success, otherwise false.
+bool hash_fd(struct hash *hash, int fd);
+
+// Add contents of a file to the hash.
+//
+// If hash debugging is enabled, the data is written verbatim to the text input
+// file.
+//
+// Returns true on success, otherwise false.
+bool hash_file(struct hash *hash, const char *fname);
+
+#endif