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fpu: Add rebias bool, value and operation

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Added the possibility of recalculating a result if it overflows or
underflows, if the result overflow and the rebias bool is true then the
intermediate result should have 3/4 of the total range subtracted from
the exponent. The same for underflow but it should be added to the
exponent of the intermediate number instead.

Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220805141522.412864-2-lucas.araujo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
This commit is contained in:
Lucas Mateus Castro (alqotel) 2022-08-05 11:15:21 -03:00 committed by Daniel Henrique Barboza
parent 0bf4d77e59
commit c40da5c6fb
3 changed files with 25 additions and 2 deletions
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21
fpu/softfloat-parts.c.inc
View file

@ -214,18 +214,35 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
p->frac_lo &= ~round_mask;
}
} else if (unlikely(exp >= exp_max)) {
flags |= float_flag_overflow | float_flag_inexact;
if (overflow_norm) {
flags |= float_flag_overflow;
if (s->rebias_overflow) {
exp -= fmt->exp_re_bias;
} else if (overflow_norm) {
flags |= float_flag_inexact;
exp = exp_max - 1;
frac_allones(p);
p->frac_lo &= ~round_mask;
} else {
flags |= float_flag_inexact;
p->cls = float_class_inf;
exp = exp_max;
frac_clear(p);
}
}
frac_shr(p, frac_shift);
} else if (unlikely(s->rebias_underflow)) {
flags |= float_flag_underflow;
exp += fmt->exp_re_bias;
if (p->frac_lo & round_mask) {
flags |= float_flag_inexact;
if (frac_addi(p, p, inc)) {
frac_shr(p, 1);
p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
exp++;
}
p->frac_lo &= ~round_mask;
}
frac_shr(p, frac_shift);
} else if (s->flush_to_zero) {
flags |= float_flag_output_denormal;
p->cls = float_class_zero;

2
fpu/softfloat.c
View file

@ -521,6 +521,7 @@ typedef struct {
typedef struct {
int exp_size;
int exp_bias;
int exp_re_bias;
int exp_max;
int frac_size;
int frac_shift;
@ -532,6 +533,7 @@ typedef struct {
#define FLOAT_PARAMS_(E) \
.exp_size = E, \
.exp_bias = ((1 << E) - 1) >> 1, \
.exp_re_bias = (1 << (E - 1)) + (1 << (E - 2)), \
.exp_max = (1 << E) - 1
#define FLOAT_PARAMS(E, F) \

4
include/fpu/softfloat-types.h
View file

@ -195,6 +195,10 @@ typedef struct float_status {
bool snan_bit_is_one;
bool use_first_nan;
bool no_signaling_nans;
/* should overflowed results subtract re_bias to its exponent? */
bool rebias_overflow;
/* should underflowed results add re_bias to its exponent? */
bool rebias_underflow;
} float_status;
#endif /* SOFTFLOAT_TYPES_H */