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+/*=============================================================================*\
+ * File: gfsmSemiring.h
+ * Author: Bryan Jurish <moocow@ling.uni-potsdam.de>
+ * Description: finite state machine library
+ *
+ * Copyright (c) 2004-2007 Bryan Jurish.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ * 
+ * This library 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
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *=============================================================================*/
+
+/** \file gfsmSemiring.h
+ *  \brief semiring types & operations
+ */
+
+#ifndef _GFSM_SEMIRING_H
+#define _GFSM_SEMIRING_H
+
+#include <gfsmCommon.h>
+#include <float.h>
+
+/*======================================================================
+ * Semiring: types
+ */
+/** Builtin semiring types
+ *  \see fsmcost(3)
+ */
+typedef enum {
+  gfsmSRTUnknown  = 0,  ///< unknown semiring (should never happen)
+  gfsmSRTBoolean  = 1,  ///< boolean semiring <set:{0,1}, plus:||, times:&&, less:>, zero:0, one:1>
+  gfsmSRTLog      = 2,  ///< negative log semiring <set:[-inf,inf], plus:-log(e^-x+e^-y), times:+, less:<, zero:inf, one:0>
+  gfsmSRTReal     = 3,  ///< real semiring: <set:[0,inf], plus:+, times:*, less:<, zero:0, one:1>
+  gfsmSRTTrivial  = 4,  ///< trivial semiring <set:{0}, plus:+, times:+, less:!=, zero:0, one:0>
+  gfsmSRTTropical = 5,  ///< tropical semiring: <set:[-inf,inf], plus:min, times:+, less:<, zero:inf, one:0>
+  gfsmSRTPLog     = 6,  ///< positive log semiring <set:[-inf,inf], plus:log(e^x+e^y), times:+, less:>, zero:-inf, one:0>
+  gfsmSRTUser     = 256 ///< user-defined semiring
+} gfsmSRType;
+
+/*======================================================================
+ * Semiring: types: structs
+ */
+/// struct to represent a builtin semi-ring for gfsm arc weights
+typedef struct {
+  gfsmSRType type;    /**< type of this semiring */
+  gfsmWeight zero;    /**< nil element of this semiring (identity for '+') */
+  gfsmWeight one;     /**< unity element of this semiring (idendity for '*') */
+} gfsmSemiring;
+
+/*======================================================================
+ * Semiring: types: functions
+ */
+/** Type for user-defined semiring unary predicates (i.e. member) */
+typedef gboolean (*gfsmSRUnaryPredicate) (gfsmSemiring *sr, gfsmWeight x);
+
+/// Type for user-defined semiring binary predicates (i.e. equal) */
+typedef gboolean (*gfsmSRBinaryPredicate) (gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+/// Type for user-defined semiring unary operations */
+typedef gfsmWeight (*gfsmSRUnaryOp) (gfsmSemiring *sr, gfsmWeight x);
+
+/// Type for user-defined semiring binary operations */
+typedef gfsmWeight (*gfsmSRBinaryOp) (gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+
+/*======================================================================
+ * Semiring: types: user structs
+ */
+/// User-defined semirings for gfsm operations
+typedef struct {
+  gfsmSemiring sr;                  /**< inheritance magic */
+
+  //-- user-defined semirings *must* set these functions
+  gfsmSRBinaryPredicate equal_func; /**< equality predicate */
+  gfsmSRBinaryPredicate less_func;  /**< order predicate */
+  gfsmSRBinaryOp        plus_func;  /**< addition operation */
+  gfsmSRBinaryOp        times_func; /**< multiplication operation */
+} gfsmUserSemiring;
+
+/*======================================================================
+ * Semiring: methods: constructors etc.
+ */
+///\name Constructors etc.
+//@{
+
+/** Create, initialize (for builtin types), and return new semiring of type \a type */
+GFSM_INLINE
+gfsmSemiring *gfsm_semiring_new(gfsmSRType type);
+
+/** Initialize and return a builtin semiring */
+GFSM_INLINE
+void gfsm_semiring_init(gfsmSemiring *sr, gfsmSRType type);
+
+/** Initialize and return a semiring */
+GFSM_INLINE
+gfsmUserSemiring *gfsm_user_semiring_new(gfsmSRBinaryPredicate equal_func,
+					 gfsmSRBinaryPredicate less_func,
+					 gfsmSRBinaryOp        plus_func,
+					 gfsmSRBinaryOp        times_func);
+
+/** Copy a semiring */
+GFSM_INLINE
+gfsmSemiring *gfsm_semiring_copy(gfsmSemiring *sr);
+
+/** Destroy a gfsmSemiring */
+GFSM_INLINE
+void gfsm_semiring_free(gfsmSemiring *sr);
+//@}
+
+/*======================================================================
+ * Semiring: general accessors
+ */
+///\name General Accessors
+//@{
+
+/** Get 'zero' element of the ::gfsmSemiring* \a sr */
+GFSM_INLINE
+gfsmWeight gfsm_sr_zero(gfsmSemiring *sr);
+
+/** Get 'one' element of the ::gfsmSemiring* \a sr */
+GFSM_INLINE
+gfsmWeight gfsm_sr_one(gfsmSemiring *sr);
+
+/** Check equality of elements \a x and \a y with respect to ::gfsmSemiring* \a sr */
+GFSM_INLINE
+gboolean gfsm_sr_equal(gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+/** Check semiring element order */
+GFSM_INLINE
+gboolean gfsm_sr_less(gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+/** 3-way comparison for semiring values */
+gint gfsm_sr_compare(gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+/** Semiring addition */
+GFSM_INLINE
+gfsmWeight gfsm_sr_plus(gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+
+/** Semiring multiplication */
+GFSM_INLINE
+gfsmWeight gfsm_sr_times(gfsmSemiring *sr, gfsmWeight x, gfsmWeight y);
+//@}
+
+/*======================================================================
+ * Semiring: methods: string utilities
+ */
+///\name String utilities
+//@{
+/** Convert symbolic name of a semiring to a gfsmSRType */
+gfsmSRType gfsm_sr_name_to_type(const char *name);
+
+/** Convert a gfsmSRType to a (constant) symbolic name */
+gchar *gfsm_sr_type_to_name(gfsmSRType type);
+//@}
+
+/*======================================================================
+ * Semiring: methods: general utilities
+ */
+///\name General utilities
+//@{
+/** stable log addition.
+ *  \returns log(exp(x)+exp(y))
+ */
+GFSM_INLINE
+gfsmWeight gfsm_log_add(gfsmWeight x, gfsmWeight y);
+//@}
+
+//-- inline definitions
+#ifdef GFSM_INLINE_ENABLED
+# include <gfsmSemiring.hi>
+#endif
+
+#endif /* _GFSM_SEMIRING_H */