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fpu/softfloat: define decompose structures 

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

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
This commit is contained in:
Alex Bennée 2017-11-27 14:02:26 +00:00
parent d97544c94a
commit a90119b5a2
1 changed files with 85 additions and 1 deletions
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86
fpu/softfloat.c
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@ -83,7 +83,6 @@ this code that are retained.
* target-dependent and needs the TARGET_* macros.
*/
#include "qemu/osdep.h"
#include "fpu/softfloat.h"
/* We only need stdlib for abort() */
@ -186,6 +185,91 @@ 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) \
.exp_size = E, \
.exp_bias = ((1 << E) - 1) >> 1, \
.exp_max = (1 << E) - 1, \
.frac_size = F, \
.frac_shift = DECOMPOSED_BINARY_POINT - F, \
.frac_lsb = 1ull << (DECOMPOSED_BINARY_POINT - F), \
.frac_lsbm1 = 1ull << ((DECOMPOSED_BINARY_POINT - F) - 1), \
.round_mask = (1ull << (DECOMPOSED_BINARY_POINT - F)) - 1, \
.roundeven_mask = (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