1 ;;;; This file contains stuff for controlling floating point traps. It
2 ;;;; is IEEE float specific, but should work for pretty much any FPU
3 ;;;; where the state fits in one word and exceptions are represented
4 ;;;; by bits being set.
6 ;;;; This software is part of the SBCL system. See the README file for
9 ;;;; This software is derived from the CMU CL system, which was
10 ;;;; written at Carnegie Mellon University and released into the
11 ;;;; public domain. The software is in the public domain and is
12 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
13 ;;;; files for more information.
17 (eval-when (:compile-toplevel :load-toplevel :execute)
19 (defconstant float-trap-alist
20 (list (cons :underflow float-underflow-trap-bit)
21 (cons :overflow float-overflow-trap-bit)
22 (cons :inexact float-inexact-trap-bit)
23 (cons :invalid float-invalid-trap-bit)
24 (cons :divide-by-zero float-divide-by-zero-trap-bit)
25 #!+x86 (cons :denormalized-operand float-denormal-trap-bit)))
27 ;;; Return a mask with all the specified float trap bits set.
28 (defun float-trap-mask (names)
31 (or (cdr (assoc x float-trap-alist))
32 (error "Unknown float trap kind: ~S." x)))
35 (defconstant rounding-mode-alist
36 (list (cons :nearest float-round-to-nearest)
37 (cons :zero float-round-to-zero)
38 (cons :positive-infinity float-round-to-positive)
39 (cons :negative-infinity float-round-to-negative)))
41 ); Eval-When (Compile Load Eval)
44 (defun floating-point-modes () (floating-point-modes))
45 (defun (setf floating-point-modes) (new) (setf (floating-point-modes) new))
47 (defun set-floating-point-modes (&key (traps nil traps-p)
48 (rounding-mode nil round-p)
49 (current-exceptions nil current-x-p)
50 (accrued-exceptions nil accrued-x-p)
51 (fast-mode nil fast-mode-p))
53 "This function sets options controlling the floating-point hardware. If a
54 keyword is not supplied, then the current value is preserved. Possible
58 A list of the exception conditions that should cause traps. Possible
59 exceptions are :UNDERFLOW, :OVERFLOW, :INEXACT, :INVALID,
60 :DIVIDE-BY-ZERO, and on the X86 :DENORMALIZED-OPERAND. Initially
61 all traps except :INEXACT are enabled.
64 The rounding mode to use when the result is not exact. Possible values
65 are :NEAREST, :POSITIVE-INFINITY, :NEGATIVE-INFINITY and :ZERO.
66 Initially, the rounding mode is :NEAREST.
70 These arguments allow setting of the exception flags. The main use is
71 setting the accrued exceptions to NIL to clear them.
74 Set the hardware's \"fast mode\" flag, if any. When set, IEEE
75 conformance or debuggability may be impaired. Some machines may not
76 have this feature, in which case the value is always NIL.
78 GET-FLOATING-POINT-MODES may be used to find the floating point modes
80 (let ((modes (floating-point-modes)))
82 (setf (ldb float-traps-byte modes) (float-trap-mask traps)))
84 (setf (ldb float-rounding-mode modes)
85 (or (cdr (assoc rounding-mode rounding-mode-alist))
86 (error "Unknown rounding mode: ~S." rounding-mode))))
88 (setf (ldb float-exceptions-byte modes)
89 (float-trap-mask current-exceptions)))
91 (setf (ldb float-sticky-bits modes)
92 (float-trap-mask accrued-exceptions)))
95 (setq modes (logior float-fast-bit modes))
96 (setq modes (logand (lognot float-fast-bit) modes))))
97 (setf (floating-point-modes) modes))
101 (defun get-floating-point-modes ()
103 "This function returns a list representing the state of the floating point
104 modes. The list is in the same format as the keyword arguments to
105 SET-FLOATING-POINT-MODES, i.e.
106 (apply #'set-floating-point-modes (get-floating-point-modes))
108 sets the floating point modes to their current values (and thus is a no-op)."
109 (flet ((exc-keys (bits)
112 ,@(mapcar #'(lambda (x)
113 `(when (logtest bits ,(cdr x))
118 (let ((modes (floating-point-modes)))
119 `(:traps ,(exc-keys (ldb float-traps-byte modes))
120 :rounding-mode ,(car (rassoc (ldb float-rounding-mode modes)
121 rounding-mode-alist))
122 :current-exceptions ,(exc-keys (ldb float-exceptions-byte modes))
123 :accrued-exceptions ,(exc-keys (ldb float-sticky-bits modes))
124 :fast-mode ,(logtest float-fast-bit modes)))))
126 (defmacro current-float-trap (&rest traps)
128 "Current-Float-Trap Trap-Name*
129 Return true if any of the named traps are currently trapped, false
131 `(not (zerop (logand ,(dpb (float-trap-mask traps) float-traps-byte 0)
132 (floating-point-modes)))))
134 ;;; Signal the appropriate condition when we get a floating-point error.
135 (defun sigfpe-handler (signal info context)
136 (declare (ignore signal info))
137 (declare (type system-area-pointer context))
138 ;; FIXME: The find-the-detailed-problem code below went stale with
139 ;; the big switchover to POSIX signal handling and signal contexts
140 ;; which are opaque at the Lisp level ca plod-0.6.7. It needs to be
141 ;; revived, which will require writing a C-level os-dependent
142 ;; function to extract floating point modes, and a Lisp-level
143 ;; DEF-ALIEN-ROUTINE to get to the C-level os-dependent function.
144 ;; Meanwhile we just say "something went wrong".
145 (error 'floating-point-exception)
147 (let* ((modes (context-floating-point-modes
148 (sb!alien:sap-alien context (* os-context-t))))
149 (traps (logand (ldb float-exceptions-byte modes)
150 (ldb float-traps-byte modes))))
151 (cond ((not (zerop (logand float-divide-by-zero-trap-bit traps)))
152 (error 'division-by-zero))
153 ((not (zerop (logand float-invalid-trap-bit traps)))
154 (error 'floating-point-invalid-operation))
155 ((not (zerop (logand float-overflow-trap-bit traps)))
156 (error 'floating-point-overflow))
157 ((not (zerop (logand float-underflow-trap-bit traps)))
158 (error 'floating-point-underflow))
159 ((not (zerop (logand float-inexact-trap-bit traps)))
160 (error 'floating-point-inexact))
162 ((zerop (ldb float-exceptions-byte modes))
163 ;; I can't tell what caused the exception!!
164 (error 'floating-point-exception
165 :traps (getf (get-floating-point-modes) :traps)))
167 (error "SIGFPE with no exceptions currently enabled?"))))
171 (defmacro with-float-traps-masked (traps &body body)
173 "Execute BODY with the floating point exceptions listed in TRAPS
174 masked (disabled). TRAPS should be a list of possible exceptions
175 which includes :UNDERFLOW, :OVERFLOW, :INEXACT, :INVALID and
176 :DIVIDE-BY-ZERO and on the X86 :DENORMALIZED-OPERAND. The respective
177 accrued exceptions are cleared at the start of the body to support
178 their testing within, and restored on exit."
179 (let ((traps (dpb (float-trap-mask traps) float-traps-byte 0))
180 (exceptions (dpb (float-trap-mask traps) float-sticky-bits 0))
181 (trap-mask (dpb (lognot (float-trap-mask traps))
182 float-traps-byte #xffffffff))
183 (exception-mask (dpb (lognot (sb!vm::float-trap-mask traps))
184 float-sticky-bits #xffffffff)))
185 `(let ((orig-modes (floating-point-modes)))
188 (setf (floating-point-modes)
189 (logand orig-modes ,(logand trap-mask exception-mask)))
191 ;; Restore the original traps and exceptions.
192 (setf (floating-point-modes)
193 (logior (logand orig-modes ,(logior traps exceptions))
194 (logand (floating-point-modes)
195 ,(logand trap-mask exception-mask))))))))