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;;; -*- Log: code.log; Package: Lisp -*-
;;;
;;; **********************************************************************
;;; This code was written as part of the Spice Lisp project at
;;; Carnegie-Mellon University, and has been placed in the public domain.
;;; If you want to use this code or any part of Spice Lisp, please contact
;;; Scott Fahlman (FAHLMAN@CMUC).
;;; **********************************************************************
;;;
;;; Functions to implement bit bashing.
;;;
;;; Written by William Lott.
;;;
(in-package "LISP")
;;;; Constants and Types.
(eval-when (compile load eval)
(defconstant unit-bits 32
"The number of bits to process at a time.")
(defconstant max-bits (ash most-positive-fixnum -2)
"The maximum number of bits that can be delt with during a single call.")
(deftype unit ()
`(unsigned-byte ,unit-bits))
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(deftype offset ()
`(integer 0 ,max-bits))
(deftype bit-offset ()
`(integer 0 (,unit-bits)))
(deftype word-offset ()
`(integer 0 (,(ceiling max-bits unit-bits))))
); eval-when
;;;; Macros for generating bit-bashing routines.
(eval-when (compile eval)
(defmacro end-bits (count)
"Returns the byte spec for COUNT bits at the end of a word, i.e. the bits
at the largest address."
(ecase vm:target-byte-order
(:little-endian `(byte ,count (- unit-bits ,count)))
(:big-endian `(byte ,count 0))))
(defmacro start-bits (count)
"Returns the byte spec for COUNT bits at the start of a word, i.e. the bits
at the smallest address."
(ecase vm:target-byte-order
(:little-endian `(byte ,count 0))
(:big-endian `(byte ,count (- unit-bits ,count)))))
(defmacro middle-bits (count where)
"Return the byte spec for COUNT bits starting at bit WHERE. WHERE of zero
corresponds to the start of the word (lowest address) and WHERE of
unit-bits corresponds to the end of the word (highest address). In other
words, act like :little-endian"
(ecase vm:target-byte-order
(:little-endian `(byte ,count ,where))
(:big-endian `(byte ,count (- unit-bits ,where ,count)))))
(defmacro bit-bash-bindings (&body guts)
`(let* ((final-bits (mod (+ len dst-bit-offset) unit-bits))
(interior (floor (- len final-bits) unit-bits)))
(declare (type bit-offset final-bits)
(type word-offset interior))
,@guts))
(defmacro bind-srcs ((kind incf-p ref-fn) &body body)
(ecase kind
(:constant `(progn
,@body
,@(when incf-p
`((incf dst-word-offset)))))
(:unary `(let ((next-1 (,ref-fn src-1 src-1-word-offset)))
(declare (type unit next-1))
,@body
,@(when incf-p
'((incf dst-word-offset)
(incf src-1-word-offset)))))
(:binary `(let ((next-1 (,ref-fn src-1 src-1-word-offset))
(next-2 (,ref-fn src-2 src-2-word-offset)))
(declare (type unit next-1 next-2))
,@body
,@(when incf-p
'((incf dst-word-offset)
(incf src-1-word-offset)
(incf src-2-word-offset)))))))
(defmacro bit-bash-loop (kind ref-fn function &optional update)
`(progn
(unless (zerop dst-bit-offset)
(bind-srcs (,kind t ,ref-fn)
(setf (ldb (end-bits (- unit-bits dst-bit-offset))
(,ref-fn dst dst-word-offset))
,function)
,update))
(dotimes (count interior)
(declare (type word-offset count))
(bind-srcs (,kind t ,ref-fn)
(setf (,ref-fn dst dst-word-offset) ,function)
,update))
(unless (zerop final-bits)
(bind-srcs (,kind nil ,ref-fn)
(setf (ldb (start-bits final-bits)
(,ref-fn dst dst-word-offset))
(ldb (start-bits final-bits)
,function))))))
(defun pick-args (op kind arg1 arg2)
(ecase kind
(:constant
op)
(:unary
(list op arg1))
(:binary
(list op arg1 arg2))))
(defmacro def-bit-basher (name op &optional (kind :binary) (ref-fn '%raw-bits))
(let ((form
`(cond
((<= (+ dst-bit-offset len) unit-bits)
;; It's narrow.
(setf (ldb (middle-bits len dst-bit-offset)
(,ref-fn dst dst-word-offset))
,(pick-args op kind
`(the unit
(ldb (middle-bits (the bit-offset len)
src-1-bit-offset)
(,ref-fn src-1 src-1-word-offset)))
`(the unit
(ldb (middle-bits (the bit-offset len)
src-2-bit-offset)
(,ref-fn src-2
src-2-word-offset))))))
(,(ecase kind
(:constant t)
(:unary '(= src-1-bit-offset dst-bit-offset))
(:binary '(= src-1-bit-offset src-2-bit-offset dst-bit-offset )))
;; Everything is aligned evenly.
(bit-bash-bindings
(bit-bash-loop ,kind ,ref-fn
,(pick-args op kind 'next-1 'next-2))))
,@(when (eq kind :binary)
`(((= src-1-bit-offset dst-bit-offset)
;; Src1 and the destination are aligned, but src2 is not.
(bit-bash-bindings
(when (> dst-bit-offset src-2-bit-offset)
(decf src-2-word-offset))
(let* ((src-2-shift
(mod (- dst-offset src-2-offset) unit-bits))
(prev-2 (,ref-fn src-2 src-2-word-offset)))
(declare (type bit-offset src-2-shift))
(declare (type unit prev-2))
(incf src-2-word-offset)
(bit-bash-loop ,kind ,ref-fn
(,op next-1 (merge-bits src-2-shift prev-2 next-2))
(setf prev-2 next-2)))))
((= src-2-bit-offset
dst-bit-offset)
;; Src2 and the destination are aligned, but src1 is not.
(bit-bash-bindings
(when (> dst-bit-offset src-1-bit-offset)
(decf src-1-word-offset))
(let* ((src-1-shift
(mod (- dst-offset src-1-offset) unit-bits))
(prev-1 (,ref-fn src-1 src-1-word-offset)))
(declare (type bit-offset src-1-shift))
(declare (type unit prev-1))
(incf src-1-word-offset)
(bit-bash-loop ,kind ,ref-fn
(,op (merge-bits src-1-shift prev-1 next-1) next-2)
(setf prev-1 next-1)))))))
,@(unless (eq kind :constant)
`((t
;; Nothing is aligned. Ack.
(bit-bash-bindings
(when (> dst-bit-offset src-1-bit-offset)
(decf src-1-word-offset))
,@(when (eq kind :binary)
'((when (> dst-bit-offset src-2-bit-offset)
(decf src-2-word-offset))))
(let* ((src-1-shift
(mod (- dst-offset src-1-offset) unit-bits))
(prev-1 (,ref-fn src-1 src-1-word-offset))
,@(when (eq kind :binary)
`((src-2-shift
(mod (- dst-offset src-2-offset) unit-bits))
(prev-2 (,ref-fn src-2 src-2-word-offset)))))
(declare (type bit-offset src-1-shift
,@(when (eq kind :binary)
'(src-2-shift)))
(type unit prev-1
,@(when (eq kind :binary) '(prev-2))))
(incf src-1-word-offset)
,@(when (eq kind :binary)
'((incf src-2-word-offset)))
(bit-bash-loop ,kind ,ref-fn
,(pick-args op kind
'(merge-bits src-1-shift prev-1 next-1)
'(merge-bits src-2-shift prev-2 next-2))
(setf prev-1 next-1
,@(when (eq kind :binary)
'(prev-2 next-2)))))))))))
(function-args '(len))
(function-decls '(len)))
(dolist (arg (ecase kind
(:constant '(dst))
(:unary '(dst src-1))
(:binary '(dst src-2 src-1))))
(let* ((name (string arg))
(offset
(intern (concatenate 'simple-string name "-OFFSET")))
(bit-offset
(intern (concatenate 'simple-string name "-BIT-OFFSET")))
(word-offset
(intern (concatenate 'simple-string name "-WORD-OFFSET"))))
(setf form
`(multiple-value-bind (,word-offset ,bit-offset)
(floor ,offset unit-bits)
(declare (type word-offset ,word-offset)
(type bit-offset ,bit-offset))
,form))
(push offset function-args)
(push offset function-decls)
(push arg function-args)))
`(defun ,name ,function-args
(declare (type offset ,@function-decls))
,form)))
); eval when
;;;; Support routines.
;;; These are compiler primitives.
(declare (type index offset))
(%raw-bits object offset))
(defun (setf %raw-bits) (object offset value)
(declare (type index offset)
(type unit value))
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(defun merge-bits (shift prev next)
"Return (ldb (byte 32 0) (ash (logior (ash prev 32) next) (- shift))) but
stay out of bignum land."
(declare (type bit-offset shift)
(type unit prev next))
(merge-bits shift prev next))
;;; These are not supported as primitives.
(proclaim '(inline 32bit-logical-eqv 32bit-logical-nand 32bit-logical-andc1
32bit-logical-andc2 32bit-logical-orc1 32bit-logical-orc2))
(defun 32bit-logical-eqv (x y)
(32bit-logical-not (32bit-logical-xor x y)))
(defun 32bit-logical-nand (x y)
(32bit-logical-not (32bit-logical-and x y)))
(defun 32bit-logical-andc1 (x y)
(32bit-logical-and (32bit-logical-not x) y))
(defun 32bit-logical-andc2 (x y)
(32bit-logical-and x (32bit-logical-not y)))
(defun 32bit-logical-orc1 (x y)
(32bit-logical-or (32bit-logical-not x) y))
(defun 32bit-logical-orc2 (x y)
(32bit-logical-or x (32bit-logical-not y)))
;;;; The actual bashers.
(proclaim '(optimize (speed 3) (safety 0)))
(def-bit-basher bit-bash-clear 0 :constant)
(def-bit-basher bit-bash-set (1- (ash 1 unit-bits)) :constant)
(def-bit-basher bit-bash-not 32bit-logical-not :unary)
(def-bit-basher bit-bash-and 32bit-logical-and)
(def-bit-basher bit-bash-ior 32bit-logical-or)
(def-bit-basher bit-bash-xor 32bit-logical-xor)
(def-bit-basher bit-bash-eqv 32bit-logical-eqv)
(def-bit-basher bit-bash-nand 32bit-logical-nand)
(def-bit-basher bit-bash-nor 32bit-logical-nor)
(def-bit-basher bit-bash-andc1 32bit-logical-andc1)
(def-bit-basher bit-bash-andc2 32bit-logical-andc2)
(def-bit-basher bit-bash-orc1 32bit-logical-orc1)
(def-bit-basher bit-bash-orc2 32bit-logical-orc2)
;;; Sap-ref-32 can be used to index into SAP objects.
(def-bit-basher system-area-clear 0 :constant sap-ref-32)
(def-bit-basher system-area-copy identity :unary sap-ref-32)