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(import (chicken base)
(chicken bitwise)
(chicken format))
(define *buffer* (make-vector (expt 2 16) #f))
(define *cursor* 0)
(define *labels* '())
;; Directives
(define (def-label sym)
(set! *labels* (cons (cons sym *cursor*) *labels*)))
(define (at-addr addr)
(unless (and (number? addr)
(>= addr 0)
(< addr (expt 2 16)))
(error "invalid addr" addr))
(set! *cursor* addr))
;; Value constructors and references
(define (label sym)
(assocdr sym *labels*))
(define (reg n)
(cond
((or (< n 0) (>= n 16)) (error "invalid arg to reg" n))
(else `(reg ,n))))
(define (imm n)
(let* ((n16 (modulo n (expt 2 16))))
`(imm ,n16)))
(define (alu-op n)
(cond
((or (< n 0) (>= n 8)) (error "invalid arg to alu-op" n))
(else `(alu-op ,n))))
(define alu-plus (alu-op 0))
(define alu-minus (alu-op 1))
(define alu-and (alu-op 2))
(define alu-or (alu-op 3))
(define alu-xor (alu-op 4))
(define alu-shl (alu-op 5))
(define alu-shr (alu-op 6))
(define alu-sar (alu-op 7))
;; Encode and emit
(define (emit . chunks)
(unless (eq? (vector-ref *buffer* *cursor*) #f)
(error "overwriting already written memory at" *cursor*))
(define word
(if (and (= (length chunks) 1)
(number? (car chunks)))
;; single argument
(car chunks)
;; multiple (bits . value) pairs
(apply encode chunks)))
(vector-set! *buffer* *cursor* word)
(set! *cursor* (+ *cursor* 1)))
(define (encode . chunks)
(let ((total-bits (apply + (map car chunks))))
(unless (= total-bits 16)
(error "emit: total bits in chunks must equal 16, got" total-bits)))
(let loop ((chs chunks) (acc 0))
(if (null? chs)
acc
(let* ((chunk (car chs))
(n (car chunk))
(val (cdr chunk)))
(when (>= val (expt 2 n))
(error "emit: value" val "does not fit in" n "bits"))
;; shift acc left by n bits and combine with val
(loop (cdr chs)
(bitwise-ior (arithmetic-shift acc n) val))))))
;; Instructions
(define (hlt)
;; just full zeros
(emit 0))
(define (alu op lhs rhs)
(unless (eq? 'alu-op (type-of op)) (error "invalid op" op))
(unless (eq? 'reg (type-of lhs)) (error "invalid lhs" lhs))
(define mode
(cond ((eq? 'reg (type-of rhs)) 0)
((eq? 'imm (type-of rhs)) 1)
(else (error "invalid rhs" rhs))))
(if (= mode 0)
;; reg mode
(emit `(4 . 1) ; opcode = 1
`(3 . ,(cadr op)) ; alu op
`(1 . ,mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . ,(cadr rhs))) ; rhs
;; immediate mode
(begin
(emit `(4 . 1) ; opcode = 1
`(3 . ,(cadr op)) ; alu op
`(1 . ,mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . 0)) ; unused
(emit `(16 . ,(cadr rhs)))) ; rhs
))
(define (add lhs rhs) (alu (alu-op 0) lhs rhs))
(define (sub lhs rhs) (alu (alu-op 1) lhs rhs))
(define (and lhs rhs) (alu (alu-op 2) lhs rhs))
(define (or lhs rhs) (alu (alu-op 3) lhs rhs))
(define (xor lhs rhs) (alu (alu-op 4) lhs rhs))
(define (shl lhs rhs) (alu (alu-op 5) lhs rhs))
(define (shr lhs rhs) (alu (alu-op 6) lhs rhs))
(define (sar lhs rhs) (alu (alu-op 7) lhs rhs))
(define (ld lhs rhs #!key (indirect #f) (pop #f))
(unless (eq? 'reg (type-of lhs)) (error "invalid lhs" lhs))
(define d-mode (if indirect 1 0))
(define p-mode (if pop 1 0))
(define m-mode
(cond ((eq? 'reg (type-of rhs)) 0)
((eq? 'imm (type-of rhs)) 1)
(else (error "invalid rhs" rhs))))
(if (= m-mode 0)
;; reg mode
(emit `(4 . 2) ; opcode = 2
`(1 . ,d-mode) ; indirect mode
`(1 . ,p-mode) ; pop mode
`(1 . 0) ; unused
`(1 . ,m-mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . ,(cadr rhs))) ; rhs
;; immediate mode
(begin
(emit `(4 . 2) ; opcode = 2
`(1 . ,d-mode) ; indirect mode
`(1 . ,p-mode) ; pop mode
`(1 . 0) ; unused
`(1 . ,m-mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . 0)) ; unused
(emit `(16 . ,(cadr rhs)))) ; rhs
))
(define (mov lhs rhs)
(unless (eq? 'reg (type-of lhs)) (error "invalid lhs" lhs))
(unless (eq? 'reg (type-of rhs)) (error "invalid rhs" rhs))
(emit `(4 . 3) ; opcode = 3
`(4 . 0) ; unused
`(4 . ,(cadr lhs)) ; lhs
`(4 . ,(cadr rhs)))) ; rhs
(define (st lhs rhs #!key (indirect #f) (push #f))
(unless (eq? 'reg (type-of lhs)) (error "invalid lhs" lhs))
(define d-mode (if indirect 1 0))
(define p-mode (if push 1 0))
(define m-mode
(cond ((eq? 'reg (type-of rhs)) 0)
((eq? 'imm (type-of rhs)) 1)
(else (error "invalid rhs" rhs))))
(if (= m-mode 0)
;; reg mode
(emit `(4 . 4) ; opcode = 4
`(1 . ,d-mode) ; indirect mode
`(1 . ,p-mode) ; pop mode
`(1 . 0) ; unused
`(1 . ,m-mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . ,(cadr rhs))) ; rhs
;; immediate mode
(begin
(emit `(4 . 4) ; opcode = 4
`(1 . ,d-mode) ; indirect mode
`(1 . ,p-mode) ; pop mode
`(1 . 0) ; unused
`(1 . ,m-mode) ; reg/imm mode
`(4 . ,(cadr lhs)) ; lhs
`(4 . 0)) ; unused
(emit `(16 . ,(cadr rhs)))) ; rhs
))
(define (br flag offset #!key (asserted #t))
(unless (eq? 'flag (type-of flag)) (error "invalid flag selector" flag))
(define asserted
(cond (#t 1)
(#f 0)
(else (error "invalid asserted bool" asserted))))
(unless (eq? 'imm (type-of offset)) (error "invalid offset" offset))
(define offset (cadr offset))
(unless (< offset (expt 2 8)) (error "offset too large" offset))
(emit `(4 . 5) ; opcode = 5
`(2 . ,(cadr flag)) ; flag selector
`(1 . 0) ; unused
`(1 . ,asserted) ; asserted (set / not set)
`(8 . ,offset)) ; offset
)
;; Utils
(define (type-of v)
(if (and (list? v)
(> (length v) 0))
(car v)
#f))
(define (assocar k alist)
(let ((v (assoc k alist)))
(and v (car v))))
(define (assocdr k alist)
(let ((v (assoc k alist)))
(and v (cdr v))))
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