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diff --git a/gnu/gas/expr.h b/gnu/gas/expr.h
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+/* expr.h -> header file for expr.c
+   Copyright (C) 1987 Free Software Foundation, Inc.
+
+This file is part of GAS, the GNU Assembler.
+
+GAS 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 1, or (at your option)
+any later version.
+
+GAS 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 GAS; see the file COPYING.  If not, write to
+the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+/*
+ * Abbreviations (mnemonics).
+ *
+ *	O	operator
+ *	Q	quantity,  operand
+ *	X	eXpression
+ */
+
+/*
+ * By popular demand, we define a struct to represent an expression.
+ * This will no doubt mutate as expressions become baroque.
+ *
+ * Currently, we support expressions like "foo-bar+42".
+ * In other words we permit a (possibly undefined) minuend, a
+ * (possibly undefined) subtrahend and an (absolute) augend.
+ * RMS says this is so we can have 1-pass assembly for any compiler
+ * emmissions, and a 'case' statement might emit 'undefined1 - undefined2'.
+ *
+ * To simplify table-driven dispatch, we also have a "segment" for the
+ * entire expression. That way we don't require complex reasoning about
+ * whether particular components are defined; and we can change component
+ * semantics without re-working all the dispatch tables in the assembler.
+ * In other words the "type" of an expression is its segment.
+ */
+
+typedef struct
+{
+	symbolS *X_add_symbol;		/* foo */
+	symbolS *X_subtract_symbol;	/* bar */
+	long int X_add_number;		/* 42.    Must be signed. */
+	segT	X_seg;			/* What segment (expr type)? */
+}
+expressionS;
+
+				/* result should be type (expressionS *). */
+#define expression(result) expr(0,result)
+
+				/* If an expression is SEG_BIG, look here */
+				/* for its value. These common data may */
+				/* be clobbered whenever expr() is called. */
+extern FLONUM_TYPE generic_floating_point_number; /* Flonums returned here. */
+				/* Enough to hold most precise flonum. */
+extern LITTLENUM_TYPE generic_bignum []; /* Bignums returned here. */
+#define SIZE_OF_LARGE_NUMBER (20)	/* Number of littlenums in above. */
+
+
+segT		expr();
+char		get_symbol_end();
+
+/* end: expr.h */