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Datei: IEEE_854_defs.pvs Sprache: PVS

Original von: PVS^©

IEEE_854_defs
  [b,p:above(1),
   alpha,E_max:integer,
   E_min:{i:integer|E_max>i}]: THEORY

  BEGIN

  IMPORTING IEEE_854_values[b,p,E_max,E_min],
            IEEE_854_remainder[b,p,alpha,E_max,E_min],
            IEEE_854_fp_int[b,p,alpha,E_max,E_min],
            arithmetic_ops[b,p,alpha,E_max,E_min],
            comparison1[b,p,E_max,E_min],
            infinity_arithmetic[b,p,E_max,E_min],
            NaN_ops[b,p,E_max,E_min],
            enumerated_type_defs

  IMPORTING reals@sqrt

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% basic instruction schemata, ignoring exceptions for now
%  These functions are listed in section 5.1 of IEEE-854

  fp,fp1,fp2: var fp_num
  mode: var rounding_mode

% Addition operator
  fp_add(fp1, fp2, mode): fp_num =
    IF finite?(fp1) & finite?(fp2)
      THEN fp_op(add, fp1, fp2, mode)
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan(add, fp1, fp2)
    ELSE fp_add_inf(fp1, fp2)
    ENDIF

% Addition operator with exceptions
  fp_add_x(fp1, fp2, mode): [fp_num, exception] =
    IF finite?(fp1) & finite?(fp2)
      THEN fp_op_x(add, fp1, fp2, mode)
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan_x(add, fp1, fp2)
    ELSE fp_add_inf_x(fp1, fp2)
    ENDIF

  fp_add_x_correct: lemma fp_add(fp1,fp2,mode) = proj_1(fp_add_x(fp1,fp2,mode))

% Subtraction Operator
  fp_sub(fp1, fp2, mode): fp_num =
    IF finite?(fp1) & finite?(fp2)
      THEN fp_op(sub, fp1, fp2, mode)
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan(sub, fp1, fp2)
    ELSE fp_sub_inf(fp1, fp2)
    ENDIF

% Subtraction Operator with exceptions
  fp_sub_x(fp1, fp2, mode): [fp_num, exception] =
    IF finite?(fp1) & finite?(fp2)
      THEN fp_op_x(sub, fp1, fp2, mode)
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan_x(sub, fp1, fp2)
    ELSE fp_sub_inf_x(fp1, fp2)
    ENDIF

% Excluding NaN operands, we should be able to prove a - b = a + (-b)
%  independent of the rounding mode
  fsub_alt_def: LEMMA
        NOT (NaN?(fp1) OR NaN?(fp2))
          => fp_sub(fp1, fp2, mode) = fp_add(fp1, toggle_sign(fp2), mode)

% Multiplication
  fp_mul(fp1, fp2, mode): fp_num =
    IF finite?(fp1) & finite?(fp2)
      THEN fp_op(mult, fp1, fp2, mode)
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan(mult, fp1, fp2)
    ELSE fp_mul_inf(fp1, fp2)
    ENDIF

% Division
  fp_div(fp1, fp2, mode): fp_num =
    IF finite?(fp1) & finite?(fp2)
      THEN IF zero?(fp2)
        THEN IF zero?(fp1)
          THEN invalid
        ELSE infinite(mult_sign(fp1, fp2))
        ENDIF
      ELSE fp_op(div, fp1, fp2, mode)
      ENDIF
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan(div, fp1, fp2)
    ELSE fp_div_inf(fp1, fp2)
    ENDIF

% Remainder (independent of rounding mode)
  fp_rem(fp1, fp2): fp_num =
    IF finite?(fp1) & finite?(fp2)
      THEN IF zero?(fp2)
        THEN invalid
      ELSE REM(fp1, fp2)
      ENDIF
    ELSIF NaN?(fp1) OR NaN?(fp2) THEN fp_nan(div, fp1, fp2)
    ELSIF infinite?(fp1) THEN invalid
    ELSE fp1
    ENDIF

% Square root

  fp_sqrt(fp, mode): fp_num =
    IF NaN?(fp) THEN NaN_sqrt(fp)
    ELSIF zero?(fp) THEN fp
    ELSIF finite?(fp)
      THEN IF sign(fp) = pos
        THEN real_to_fp(fp_round(sqrt(value(fp)), mode))
      ELSE invalid
      ENDIF
    ELSIF i_sign(fp) = pos THEN fp
    ELSE invalid
    ENDIF

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% bug test spec, won't typecheck,
%% cannot determine full theory instance
%  fp_id(fp):fp_num =
%    cases fp of
%      finite(s,e,d): fp,
%      infinite(s): fp,
%      NaN(sig,data):fp
%    endcases

  END IEEE_854_defs

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