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(define-library (csc encoding)
(export encode)
(import (scheme base)
(only (csc loop)
loop
return)
(only (csc match) match))
(begin
; I'm only going to say this once, so pay attention.
; The format of unboxed constants is described in bytecocde/src/data.rs.
; Boxed values are represented by a pointer to an array on the heap. The
; first position in the array is an integer code indicating what type the
; object is. Vectors have code 0, codes for other types are not stable.
; Vectors are represented as an array, the first element of which is the
; integer 0 (the type code), the second element is the vector length, and
; the remaining slots hold the array values.
(define (low-byte w n)
(write-u8 (remainder n #x100) w))
(define (64->le-bytes w n)
(low-byte w n)
(low-byte w (quotient n #x100))
(low-byte w (quotient n #x10000))
(low-byte w (quotient n #x1000000))
(low-byte w (quotient n #x100000000))
(low-byte w (quotient n #x10000000000))
(low-byte w (quotient n #x1000000000000))
(low-byte w (quotient n #x100000000000000)))
; Bitwise-negates a 63-bit unsigned integer.
(define (bitwise-not n)
(loop with n* = 0
for i from 1 to 63
for n = n then (quotient n 2)
for digit = 1 then (* 2 digit)
if (even? n)
do (set! n* (+ n* digit))
finally (return n*)))
(define (int->le-bytes w n)
(when (or (>= n #x4000000000000000)
(< n #x-4000000000000000))
(error "int constant too large" n))
(when (negative? n)
(set! n (remainder
(+ 1 (bitwise-not (- n)))
#x8000000000000000)))
(64->le-bytes w (+ 1 (* 2 n))))
(define (bool->le-bytes w b)
(if b
(64->le-bytes w #xa)
(64->le-bytes w #x2)))
(define (const->le-bytes w x)
(cond
((integer? x)
(int->le-bytes w x))
((boolean? x)
(bool->le-bytes w x))
((null? x)
(64->le-bytes w #x12))
(else (error "unexpected type in const->le-bytes" x))))
(define (make-opcode w code arg1-const arg2-const)
(when (>= code #x40)
(error "code is more than 6 bits" code))
(define arg1-bit (if arg1-const
2
0))
(define arg2-bit (if arg2-const
1
0))
(write-u8 (+ (* 4 code) arg1-bit arg2-bit) w))
(define (arg->le-bytes w atom)
(match atom
(('const val) (const->le-bytes w val))
(('local i)
(when (>= i #x100)
(error "local index is out of range" i))
(write-u8 i w))
(_ (error "unexpected form in arg->le-bytes" atom))))
(define (is-const? atom)
(match atom
(('const _) #t)
(_ #f)))
(define (opcode-switch w opcode)
(match opcode
(('mov dest src)
(make-opcode w 0 (is-const? src) #f)
(arg->le-bytes w dest)
(arg->le-bytes w src))
(('jmpif test dest)
(make-opcode w 1 (is-const? test) (is-const? dest))
(arg->le-bytes w test)
(arg->le-bytes w dest))
(('jmp dest)
(make-opcode w 2 (is-const? dest) #f)
(arg->le-bytes w dest))
(('alloc dest size)
(make-opcode w 3 (is-const? size) #f)
(arg->le-bytes w dest)
(arg->le-bytes w size))
(('peek dest ptr offset)
(make-opcode w 4 (is-const? ptr) (is-const? offset)) ; ptr will likely never be constant.
(arg->le-bytes w dest)
(arg->le-bytes w ptr)
(arg->le-bytes w offset))
(('poke word ('local ptr) offset)
; We only have 2 bits to store whether the arguments are const, but
; it's actually true that a pointer can never be a constant. So we
; only track whether the word and offset arguments are constant, and
; assume ptr will always be a one-byte register name.
(make-opcode w 5 (is-const? word) (is-const? offset))
(arg->le-bytes w word)
(arg->le-bytes w (list 'local ptr))
(arg->le-bytes w offset))
(('add dest x y)
(make-opcode w 6 (is-const? x) (is-const? y))
(arg->le-bytes w dest)
(arg->le-bytes w x)
(arg->le-bytes w y))
(('sub dest x y)
(make-opcode w 7 (is-const? x) (is-const? y))
(arg->le-bytes w dest)
(arg->le-bytes w x)
(arg->le-bytes w y))
(('mul dest x y)
(make-opcode w 8 (is-const? x) (is-const? y))
(arg->le-bytes w dest)
(arg->le-bytes w x)
(arg->le-bytes w y))
(('div dest x y)
(make-opcode w 9 (is-const? x) (is-const? y))
(arg->le-bytes w dest)
(arg->le-bytes w x)
(arg->le-bytes w y))
(('mod dest x y)
(make-opcode w 10 (is-const? x) (is-const? y))
(arg->le-bytes w dest)
(arg->le-bytes w x)
(arg->le-bytes w y))
(('peekbyte dest ptr offset)
(make-opcode w 11 (is-const? ptr) (is-const? offset))
(arg->le-bytes w dest)
(arg->le-bytes w ptr)
(arg->le-bytes w offset))
(('pokebyte word ('local ptr) offset)
(make-opcode w 12 (is-const? word) (is-const? offset))
(arg->le-bytes w word)
(arg->le-bytes w (list 'local ptr))
(arg->le-bytes w offset))
(('exit code)
(make-opcode w 13 (is-const? code) #f)
(arg->le-bytes w code))
(('alloc-bytevector dest size)
(make-opcode w 14 (is-const? size) #f)
(arg->le-bytes w dest)
(arg->le-bytes w size))
(('typeof dest x)
(make-opcode w 15 (is-const? x) #f)
(arg->le-bytes w dest)
(arg->le-bytes w x))
(_ (error "invalid opcode" opcode))))
(define (encode program)
(define out (open-output-bytevector))
(map (lambda (op) (opcode-switch out op)) program)
(get-output-bytevector out))))
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