From c985522b322b1aca22691d3bf8ffad5ac2779151 Mon Sep 17 00:00:00 2001
From: Chris Hanson <org/chris-hanson/cph>
Date: Mon, 29 Sep 2008 05:41:51 +0000
Subject: [PATCH] Implement procedures to control flonum rounding mode.

---
 v7/src/runtime/fixart.scm  | 57 ++++++++++++++++++++++++++++++++++++--
 v7/src/runtime/runtime.pkg |  6 +++-
 2 files changed, 60 insertions(+), 3 deletions(-)

diff --git a/v7/src/runtime/fixart.scm b/v7/src/runtime/fixart.scm
index 2f3d2848f..e14b85a11 100644
--- a/v7/src/runtime/fixart.scm
+++ b/v7/src/runtime/fixart.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: fixart.scm,v 1.20 2008/02/14 02:35:02 cph Exp $
+$Id: fixart.scm,v 1.21 2008/09/29 05:41:48 cph Exp $
 
 Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
     1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
@@ -152,4 +152,57 @@ USA.
 
 (define (->flonum x)
   (guarantee-real x '->FLONUM)
-  (exact->inexact (real-part x)))
\ No newline at end of file
+  (exact->inexact (real-part x)))
+
+(define-primitives
+  (float-rounding-modes 0)
+  (get-float-rounding-mode 0)
+  (set-float-rounding-mode 1))
+
+(define float-rounding-mode-names
+  '#(TO-NEAREST TOWARD-ZERO DOWNWARD UPWARD))
+
+(define (flo:rounding-modes)
+  (let ((n (vector-length float-rounding-mode-names))
+	(m (float-rounding-modes)))
+    (let loop ((i 0) (names '()))
+      (if (fix:< i n)
+	  (loop (fix:+ i 1)
+		(if (fix:= (fix:and (fix:lsh 1 i) m) 0)
+		    names
+		    (cons (vector-ref float-rounding-mode-names i) names)))
+	  names))))
+
+(define (flo:rounding-mode)
+  (let ((m (get-float-rounding-mode)))
+    (if (not (fix:< m (vector-length float-rounding-mode-names)))
+	(error "Unknown float rounding mode:" m))
+    (vector-ref float-rounding-mode-names m)))
+
+(define (flo:set-rounding-mode! mode)
+  (set-float-rounding-mode (%mode-name->number mode 'FLO:SET-ROUNDING-MODE!)))
+
+(define (flo:with-rounding-mode mode thunk)
+  (let ((inside-mode (%mode-name->number mode 'FLO:WITH-ROUNDING-MODE))
+	(outside-mode))
+    (shallow-fluid-bind (lambda ()
+			  (set! outside-mode (get-float-rounding-mode))
+			  (set-float-rounding-mode inside-mode)
+			  (set! inside-mode)
+			  unspecific)
+			thunk
+			(lambda ()
+			  (set! inside-mode (get-float-rounding-mode))
+			  (set-float-rounding-mode outside-mode)
+			  (set! outside-mode)
+			  unspecific))))
+
+(define (%mode-name->number mode caller)
+  (guarantee-interned-symbol mode caller)
+  (let ((n (vector-length float-rounding-mode-names)))
+    (let loop ((i 0))
+      (if (not (fix:< i n))
+	  (error:bad-range-argument mode caller))
+      (if (eq? mode (vector-ref float-rounding-mode-names i))
+	  i
+	  (loop (fix:+ i 1))))))
\ No newline at end of file
diff --git a/v7/src/runtime/runtime.pkg b/v7/src/runtime/runtime.pkg
index 4d9c68d15..c482d5631 100644
--- a/v7/src/runtime/runtime.pkg
+++ b/v7/src/runtime/runtime.pkg
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: runtime.pkg,v 14.687 2008/09/24 05:57:00 cph Exp $
+$Id: runtime.pkg,v 14.688 2008/09/29 05:41:51 cph Exp $
 
 Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
     1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
@@ -239,6 +239,9 @@ USA.
 	  flo:positive?
 	  flo:round
 	  flo:round->exact
+	  flo:rounding-mode
+	  flo:rounding-modes
+	  flo:set-rounding-mode!
 	  flo:sin
 	  flo:sqrt
 	  flo:tan
@@ -248,6 +251,7 @@ USA.
 	  flo:vector-length
 	  flo:vector-ref
 	  flo:vector-set!
+	  flo:with-rounding-mode
 	  flo:zero?
 	  guarantee-index-fixnum
 	  guarantee-limited-index-fixnum
-- 
2.25.1