path: root/cpu/alu.ml

open Netlist_gen

let zeroes n =
    const (String.make n '0')

let one n =
    const "1" ++ zeroes (n-1)
let two n =
    const "01" ++ zeroes (n-2)

let rec rep n k =
    if n = 1 then k
    else
        let s = rep (n/2) k in
        if n mod 2 = 0 then s ++ s else s ++ s ++ k

let rec eq_c n v c = (* v is a value, c is a constant *)
    if n = 1 then
        if c = 1 then v else not v
    else
        (eq_c 1 (v ** 0) (c mod 2)) ^& (eq_c (n-1) (v % (1, n-1)) (c/2))

let rec all1 n x =
    if n = 1 then
        x
    else
        (x ** 0) ^& (all1 (n-1) (x % (1, n-1)))

let rec nonnull n a =
    if n = 1 then
        a
    else
        (a ** 0) ^| (nonnull (n-1) (a % (1, n-1)))

let rec sign_extend n_a n_dest a =
    a ++ rep (n_dest - n_a) (a ** (n_a - 1))

(* Arithmetic operations *)

let fulladder a b c =
       let s = a ^^ b ^^ c in
       let r = (a ^& b) ^| ((a ^^ b) ^& c) in
       s, r

let rec nadder_with_carry n a b c_in =
    if n = 1 then fulladder a b c_in
    else 
        let s_n, c_n1 = fulladder (a ** 0) (b ** 0) c_in in
        let s_n1, c_out = nadder_with_carry (n-1) (a % (1, n-1)) (b % (1, n-1)) c_n1 in
        s_n ++ s_n1, c_out

let nadder n a b =
    let a, b = nadder_with_carry n a b (const "0") in
    b ^. a

let rec nsubber n a b =
    zeroes n (* TODO *)

let rec nmul n a b start_signal =
    zeroes n, zeroes n, start_signal (* TODO : retuns lo and hi part of 32-bit answer *)

let rec ndiv n a b start_signal =
    zeroes n, zeroes n, start_signal (* TODO : returns quotient and remainder *)

let rec nmulu n a b start_signal =
    zeroes n, zeroes n, start_signal (* TODO : same as nmul but unsigned *)

let rec ndivu n a b start_signal =
    zeroes n, zeroes n, start_signal (* TODO : save as ndiv but unsigned *)

(* Shifts *)

let npshift_signed n p a b =
    a (* TODO (here b is a signed integer on p bits) *)

let op_lsl n a b =
    a (* TODO (b is unsigned, same size n) *)

let op_lsr n a b =
    a (* TODO (b is unsigned, same size n) *)

let op_asr n a b =
    a (* TODO (b unsigned size n) *)

(* Comparisons *)

let rec eq_n n a b =
    all1 n (not (a ^^ b))

let rec ne_n n a b =
    nonnull n (a ^^ b)

let rec lt_n n a b =
    const "0"       (* TODO : less than *)

let rec ult_n n a b =
    const "0"       (* TODO : less than, unsigned *)

let rec le_n n a b =
    const "0"       (* TODO : less than or equal *)

let rec ule_n n a b =
    const "0"       (* TODO : less than or equal, unsigned *)

(* Big pieces *)

let alu_comparer n f0 f a b =
    (*
        f0  f   action
        --  -   ------
        0   0   equal
        0   1   not equal
        0   2   equal
        0   3   not equal
        1   0   lt
        1   1   le
        1   2   lt unsigned
        1   3   le unsigned
    *)
    let eq_ne = mux (f ** 0) (eq_n n a b) (ne_n n a b) in
    let lte_signed = mux (f ** 0) (lt_n n a b) (le_n n a b) in
    let lte_unsigned = mux (f ** 0) (ult_n n a b) (ule_n n a b) in
    let lte = mux (f ** 1) lte_signed lte_unsigned in
    mux f0 eq_ne lte

let alu_arith f1 f a b start_signal =
    (*  See table for ALU below *)
    let add = nadder 16 a b in
    let sub = nsubber 16 a b in
    let mul, mul2, mul_end_signal = nmul 16 a b start_signal in
    let div, div2, div_end_signal = ndiv 16 a b start_signal in
    let mulu, mulu2, mulu_end_signal = nmulu 16 a b start_signal in
    let divu, divu2, divu_end_signal = ndivu 16 a b start_signal in
    let q00 = mux (f ** 0) add sub in
    let q01 = mux (f ** 0) mul div in
    let q03 = mux (f ** 0) mulu divu in
    let q10 = mux (f ** 1) q00 q01 in
    let q11 = mux (f ** 1) q00 q03 in
    let q = mux f1 q10 q11 in
    let r01 = mux (f ** 0) mul2 div2 in
    let r03 = mux (f ** 0) mulu2 divu2 in
    let r10 = mux (f ** 1) (zeroes 16) r01 in
    let r11 = mux (f ** 1) (zeroes 16) r03 in
    let r = mux f1 r10 r11 in
    let s01 = mux (f ** 0) mul_end_signal div_end_signal in
    let s03 = mux (f ** 0) mulu_end_signal divu_end_signal in
    let s10 = mux (f ** 1) start_signal s01 in
    let s11 = mux (f ** 1) start_signal s03 in
    let end_signal = mux f1 s10 s11 in
    q, r, end_signal

let alu_logic f a b =
    (*  See table for ALU below *)
    let q0 = mux (f ** 0) (a ^| b) (a ^& b) in
    let q1 = mux (f ** 0) (a ^^ b) (not (a ^| b)) in
    mux (f ** 1) q0 q1

let alu_shifts f a b =
    (*  See table for ALU below *)
    let q1 = mux (f ** 0) (op_lsr 16 a b) (op_asr 16 a b) in
    mux (f ** 1) (op_lsl 16 a b) q1

let alu f1 f0 f a b start_signal =
    (*
        f0  f1  f   action
        --  --  -   ------
        0   0   0   add
        0   0   1   sub
        0   0   2   mul
        0   0   3   div
        0   1   0   addu
        0   1   1   subu
        0   1   2   mulu
        0   1   3   divu
        1   0   0   or
        1   0   1   and
        1   0   2   xor
        1   0   3   nor
        1   1   0   lsl
        1   1   1   lsl
        1   1   2   lsr
        1   1   3   asr
    *)
    let arith, arith_r, arith_end_signal = alu_arith f1 f a b start_signal in
    let logic = alu_logic f a b in
    let shifts = alu_shifts f a b in

    let q0 = mux f1 logic shifts in
    let s = mux f0 arith q0 in
    let r = mux f0 arith_r (zeroes 16) in
    let end_signal = mux f0 arith_end_signal start_signal in
    s, r, end_signal