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fpu/softfloat: define decompose structures

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These structures pave the way for generic softfloat helper routines
that will operate on fully decomposed numbers.

Backports commit a90119b5a2c174250601be6503b91e5c9df6e83b from qemu
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Alex Bennée 2018-03-08 10:06:23 -05:00 committed by Lioncash
parent 562f14adcc
commit d80f1ea222
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qemu/fpu/softfloat.c
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@ -186,6 +186,91 @@ static inline flag extractFloat64Sign(float64 a)
return float64_val(a) >> 63;
}
/*
* Classify a floating point number. Everything above float_class_qnan
* is a NaN so cls >= float_class_qnan is any NaN.
*/
typedef enum __attribute__ ((__packed__)) {
float_class_unclassified,
float_class_zero,
float_class_normal,
float_class_inf,
float_class_qnan, /* all NaNs from here */
float_class_snan,
float_class_dnan,
float_class_msnan, /* maybe silenced */
} FloatClass;
/*
* Structure holding all of the decomposed parts of a float. The
* exponent is unbiased and the fraction is normalized. All
* calculations are done with a 64 bit fraction and then rounded as
* appropriate for the final format.
*
* Thanks to the packed FloatClass a decent compiler should be able to
* fit the whole structure into registers and avoid using the stack
* for parameter passing.
*/
typedef struct {
uint64_t frac;
int32_t exp;
FloatClass cls;
bool sign;
} FloatParts;
#define DECOMPOSED_BINARY_POINT (64 - 2)
#define DECOMPOSED_IMPLICIT_BIT (1ull << DECOMPOSED_BINARY_POINT)
#define DECOMPOSED_OVERFLOW_BIT (DECOMPOSED_IMPLICIT_BIT << 1)
/* Structure holding all of the relevant parameters for a format.
* exp_size: the size of the exponent field
* exp_bias: the offset applied to the exponent field
* exp_max: the maximum normalised exponent
* frac_size: the size of the fraction field
* frac_shift: shift to normalise the fraction with DECOMPOSED_BINARY_POINT
* The following are computed based the size of fraction
* frac_lsb: least significant bit of fraction
* fram_lsbm1: the bit bellow the least significant bit (for rounding)
* round_mask/roundeven_mask: masks used for rounding
*/
typedef struct {
int exp_size;
int exp_bias;
int exp_max;
int frac_size;
int frac_shift;
uint64_t frac_lsb;
uint64_t frac_lsbm1;
uint64_t round_mask;
uint64_t roundeven_mask;
} FloatFmt;
/* Expand fields based on the size of exponent and fraction */
#define FLOAT_PARAMS(E, F) \
E, \
((1 << E) - 1) >> 1, \
(1 << E) - 1, \
F, \
DECOMPOSED_BINARY_POINT - F, \
1ull << (DECOMPOSED_BINARY_POINT - F), \
1ull << ((DECOMPOSED_BINARY_POINT - F) - 1), \
(1ull << (DECOMPOSED_BINARY_POINT - F)) - 1, \
(2ull << (DECOMPOSED_BINARY_POINT - F)) - 1
static const FloatFmt float16_params = {
FLOAT_PARAMS(5, 10)
};
static const FloatFmt float32_params = {
FLOAT_PARAMS(8, 23)
};
static const FloatFmt float64_params = {
FLOAT_PARAMS(11, 52)
};
/*----------------------------------------------------------------------------
| Takes a 64-bit fixed-point value `absZ' with binary point between bits 6
| and 7, and returns the properly rounded 32-bit integer corresponding to the