HP3000/hp3000_cpu_fp.h

/* hp3000_cpu_fp.h: HP 3000 floating-point interface declarations

   Copyright (c) 2016, J. David Bryan

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   11-Jun-16    JDB     Bit mask constants are now unsigned
   21-Jan-16    JDB     First release version
   29-Mar-15    JDB     Created


   This file contains declarations used by the CPU to interface with the
   floating-point operations executor.
*/



/* Program constants */

#define SIGN_BIT            0100000u
#define EXPONENT_BITS       0077700u
#define ASSUMED_BIT         0000100u
#define FRACTION_BITS       0000077u


/* Operand precisions:

    - S = 1-word integer
    - D = 2-word integer
    - F = 2-word single-precision floating-point
    - X = 3-word extended-precision floating-point
    - E = 4-word double-precision floating-point


   Implementation notes:

    1. The ordering of the enumeration constants is important, as we depend on
       the "fp" type codes to reflect the number of words used by the packed
       representation.
*/

typedef enum {
    in_s = 0,                                   /* 1-word integer */
    in_d = 1,                                   /* 2-word integer */
    fp_f = 2,                                   /* 2-word single-precision floating-point */
    fp_x = 3,                                   /* 3-word extended-precision floating-point */
    fp_e = 4                                    /* 4-word double-precision floating-point */
    } FP_OPSIZE;


/* Conversion from operand size to word count */

#define TO_COUNT(s)     ((uint32) (s + (s < fp_f)))


/* Floating point operations */

typedef enum {
    fp_add,
    fp_sub,
    fp_mpy,
    fp_div,
    fp_flt,
    fp_fixr,
    fp_fixt
    } FP_OPR;


/* General operand.

   An in-memory representation of an integer or packed floating-point number.
   An actual value will use one, two, three, or four words, as indicated by the
   "precision" specified.

   "trap" is significant only for result values; it is ignored for operand
   values.  A good result will have trap_None.
*/

typedef struct {
    HP_WORD    words [4];                       /* integer or floating-point value */
    FP_OPSIZE  precision;                       /* operand size descriptor */
    uint32     trap;                            /* validity of the result */
    } FP_OPND;


/* Special operands */

static const FP_OPND FP_NOP = { { 0, 0, 0, 0 }, in_s, trap_None };    /* an unneeded operand */


/* Floating-point global routines */

extern FP_OPND fp_exec (FP_OPR operator, FP_OPND left, FP_OPND right);