From 11da511c784eca003deb90c23570f0873954e0de Mon Sep 17 00:00:00 2001
From: Duncan Wilkie <antigravityd@gmail.com>
Date: Sat, 18 Nov 2023 06:11:09 -0600
Subject: Initial commit.

---
 ic-reals-6.3/base/strictAlt.c | 129 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 ic-reals-6.3/base/strictAlt.c

(limited to 'ic-reals-6.3/base/strictAlt.c')

diff --git a/ic-reals-6.3/base/strictAlt.c b/ic-reals-6.3/base/strictAlt.c
new file mode 100644
index 0000000..9ae4434
--- /dev/null
+++ b/ic-reals-6.3/base/strictAlt.c
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2000, Imperial College
+ *
+ * This file is part of the Imperial College Exact Real Arithmetic Library.
+ * See the copyright notice included in the distribution for conditions
+ * of use.
+ */
+
+#include <stdio.h>
+#include "real.h"
+#include "real-impl.h"
+
+/*
+ * The conditional is implemented as a function:
+ *
+ *  void * realAlt(Bool, *void, ...)
+ * 
+ * where the arguments are a list of guard/value pairs. This is implemented
+ * using stdarg(3). The last guard must be the constant DEFAULT_GUARD.
+ */
+
+typedef struct ALT_CELL {
+	Bool guard;
+	void *value;
+	struct ALT_CELL *next;
+} AltCell;
+
+#include <stdarg.h>
+
+/*
+ * ### A better scheme would be to put the alt in the heap as well. Perhaps
+ * later.
+ */
+void *
+realAlt(Bool guard, void *value, ...)
+{
+	va_list ap;
+	AltCell *head, *ptr;
+	AltCell **prev;
+	void *defaultValue;
+	void runStack();
+
+	/*
+	 * The caller is a wally if the first argument is the default guard.
+	 * But we accept it.
+	 */
+	if ((unsigned) guard == DEFAULT_GUARD)
+		return value;
+
+	if (guard->gen.tag.value == LAZY_TRUE)
+		return value;
+
+	if ((head = (AltCell *) alloca(sizeof(AltCell))) == NULL)
+		Error(FATAL, E_INT, "realAlt", "alloca failed");
+
+	head->guard = guard;
+	head->value = value;
+	head->next = NULL;
+	ptr = head;
+
+	/*
+	 * Now we consume the arguments. Each is a guard/value pair. If
+	 * the guard is true, then we just return the value. If not then
+	 * we allocate a cell with the guard and value and add it to
+	 * the list of cells.
+	 */
+	va_start(ap, value);
+	while ((unsigned) (guard = va_arg(ap, Bool)) != DEFAULT_GUARD) {
+		value = va_arg(ap, void *);
+
+		if (guard->gen.tag.value == LAZY_TRUE)
+			return value;
+
+		if ((ptr->next = (AltCell *) alloca(sizeof(AltCell))) == NULL)
+			Error(FATAL, E_INT, "realAlt", "alloca failed");
+
+		ptr = ptr->next;
+		ptr->guard = guard;
+		ptr->value = value;
+		ptr->next = NULL;
+	}
+	defaultValue = va_arg(ap, void *);
+	va_end(ap);
+
+	/*
+	 * If we reach here, then we have a list of AltCells which
+	 * have guards having value LAZY_UNKNOWN. We now walk down this
+	 * list repeatedly. For each alternative, we force the next value
+	 * in the boolean stream. If any guard becomes true, then we
+	 * return the corresponding value. If something becomes false,
+	 * it gets removed from the list. The loop ends when the list
+	 * becomes empty whereupon we return the default value provided
+	 * at the end of the argument list.
+	 */
+	ptr = head;
+	prev = &head;
+	while (ptr != NULL) {
+		if (ptr->guard->gen.tag.value == LAZY_UNKNOWN) {
+			PUSH_2(ptr->guard->gen.force, ptr->guard);
+			runStack();
+		}
+		switch (ptr->guard->gen.tag.value) {
+			case LAZY_TRUE :
+				return ptr->value;
+				break;
+			case LAZY_FALSE :
+				*prev = ptr->next; /* unlink the cell */
+				ptr = ptr->next;
+				break;
+			case LAZY_UNKNOWN :
+				prev = &(ptr->next);
+				ptr = ptr->next;
+				break;
+			default :
+				Error(FATAL, E_INT, "realAlt",
+								"invalid boolean value encountered");
+				break;
+		}
+
+		/*
+		 * Reached the end of the list so start from the beginning again.
+		 */
+		if (ptr == NULL) {
+			ptr = head;
+			prev = &head;
+		}
+	}
+	return defaultValue;
+}
-- 
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