;;; *not* return the second value of truncate, so it must be computed by the
;;; caller if needed.
;;;
-;;; In the float case, we pick off small arguments so that compiler can use
-;;; special-case operations. We use an exclusive test, since (due to round-off
-;;; error), (float most-positive-fixnum) may be greater than
-;;; most-positive-fixnum.
+;;; In the float case, we pick off small arguments so that compiler
+;;; can use special-case operations. We use an exclusive test, since
+;;; (due to round-off error), (float most-positive-fixnum) is likely
+;;; to be equal to (1+ most-positive-fixnum). An exclusive test is
+;;; good enough, because most-positive-fixnum will be one less than a
+;;; power of two, and that power of two will be exactly representable
+;;; as a float (at least until we get 128-bit fixnums).
(defun %unary-truncate (number)
(number-dispatch ((number real))
((integer) number)
;;; Specialized versions for floats.
(macrolet ((def (type name)
`(defun ,name (number)
- (if (< ,(coerce most-negative-fixnum type)
+ (if (< ,(coerce sb!xc:most-negative-fixnum type)
number
- ,(coerce most-positive-fixnum type))
+ ,(coerce sb!xc:most-positive-fixnum type))
(truly-the fixnum (,name number))
;; General -- slow -- case.
(multiple-value-bind (bits exp) (integer-decode-float number)
(truly-the fixnum (%unary-round number))
(multiple-value-bind (bits exp) (integer-decode-float number)
(let* ((shifted (ash bits exp))
- (rounded (if (and (minusp exp)
- (oddp shifted)
- (eql (logand bits
- (lognot (ash -1 (- exp))))
- (ash 1 (- -1 exp))))
- (1+ shifted)
+ (rounded (if (minusp exp)
+ (let ((fractional-bits (logand bits (lognot (ash -1 (- exp)))))
+ (0.5bits (ash 1 (- -1 exp))))
+ (cond
+ ((> fractional-bits 0.5bits) (1+ shifted))
+ ((< fractional-bits 0.5bits) shifted)
+ (t (if (oddp shifted) (1+ shifted) shifted))))
shifted)))
(if (minusp number)
(- rounded)