Rearrange the file tree.

[u/mdw/catacomb] / base / ct.h

/* -*-c-*-
 *
 * Constant-time operations
 *
 * (c) 2013 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb 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 Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#ifndef CATACOMB_CT_H
#define CATACOMB_CT_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

#include <mLib/bits.h>

/*----- Functions provided ------------------------------------------------*/

/* --- @ct_inteq@ --- *
 *
 * Arguments:	@uint32 x, y@ = two 32-bit unsigned integers
 *
 * Returns:	One if @x@ and @y@ are equal, zero if they differ.
 *
 * Use:		Answers whether two integers are equal, in constant time.
 */

extern int ct_inteq(uint32 /*x*/, uint32 /*y*/);

/* --- @ct_intle@ --- *
 *
 * Arguments:	@uint32 x, y@ = two 32-bit unsigned integers
 *
 * Returns:	One if %$x \le y$% are equal, zero if @x@ is greater.
 *
 * Use:		Answers whether two integers are ordered, in constant time.
 */

extern int ct_intle(uint32 /*x*/, uint32 /*y*/);

/* --- @ct_pick@ --- *
 *
 * Arguments:	@uint32 a@ = a switch, either zero or one
 *		@uint32 x0, x1@ = two 32-bit unsigned integers
 *
 * Returns:	@x0@ if @a@ is zero; @x1@ if @a@ is one.  Other values of @a@
 *		will give you unhelpful results.
 *
 * Use:		Picks one of two results according to a switch variable, in
 *		constant time.
 */

extern int ct_pick(uint32 /*a*/, uint32 /*x0*/, uint32 /*x1*/);

/* --- @ct_condcopy@ --- *
 *
 * Arguments:	@uint32 a@ = a switch, either zero or one
 *		@void *d@ = destination pointer
 *		@const void *s@ = source pointer
 *		@size_t n@ amount to copy
 *
 * Returns:	---
 *
 * Use:		If @a@ is one then copy the @n@ bytes starting at @s@ to
 *		@d@; if @a@ is zero then leave @d@ unchanged (but it will
 *		still be written).  All of this is done in constant time.
 */

extern void ct_condcopy(uint32 /*a*/,
			void */*d*/, const void */*s*/, size_t /*n*/);

/* --- @ct_memeq@ ---
 *
 * Arguments:	@const void *p, *q@ = two pointers to buffers
 *		@size_t n@ = the (common) size of the buffers
 *
 * Returns:	One if the two buffers are equal, zero if they aren't.
 *
 * Use:		Compares two chunks of memory, in constant time.
 */

extern int ct_memeq(const void */*p*/, const void */*q*/, size_t /*n*/);

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif