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diff --git a/gas/subsegs.h b/gas/subsegs.h
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+/* subsegs.h -> subsegs.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.  */
+
+/*
+ * For every sub-segment the user mentions in the ASsembler program,
+ * we make one struct frchain. Each sub-segment has exactly one struct frchain
+ * and vice versa.
+ *
+ * Struct frchain's are forward chained (in ascending order of sub-segment
+ * code number). The chain runs through frch_next of each subsegment.
+ * This makes it hard to find a subsegment's frags
+ * if programmer uses a lot of them. Most programs only use text0 and
+ * data0, so they don't suffer. At least this way:
+ * (1)	There are no "arbitrary" restrictions on how many subsegments
+ *	can be programmed;
+ * (2)	Subsegments' frchain-s are (later) chained together in the order in
+ *	which they are emitted for object file viz text then data.
+ *
+ * From each struct frchain dangles a chain of struct frags. The frags
+ * represent code fragments, for that sub-segment, forward chained.
+ */
+
+struct frchain			/* control building of a frag chain */
+{				/* FRCH = FRagment CHain control */
+  struct frag *	frch_root;	/* 1st struct frag in chain, or NULL */
+  struct frag *	frch_last;	/* last struct frag in chain, or NULL */
+  struct frchain * frch_next;	/* next in chain of struct frchain-s */
+  segT		frch_seg;	/* SEG_TEXT or SEG_DATA. */
+  subsegT	frch_subseg;	/* subsegment number of this chain */
+};
+
+typedef struct frchain frchainS;
+
+extern frchainS * frchain_root;	/* NULL means no frchains yet. */
+				/* all subsegments' chains hang off here */
+
+extern frchainS * frchain_now;
+				/* Frchain we are assembling into now */
+				/* That is, the current segment's frag */
+				/* chain, even if it contains no (complete) */
+				/* frags. */
+
+extern frchainS * data0_frchainP;
+				/* Sentinel for frchain crawling. */
+				/* Points to the 1st data-segment frchain. */
+				/* (Which is pointed to by the last text- */
+				/* segment frchain.) */
+
+/* end: subsegs.h */