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py/formatfloat: Use pow(10, e) instead of pos/neg_pow lookup tables.

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Rework the conversion of floats to decimal strings so it aligns precisely
with the conversion of strings to floats in parsenum.c.  This is to avoid
rendering 1eX as 9.99999eX-1 etc.  This is achieved by removing the power-
of-10 tables and using pow() to compute the exponent directly, and that's
done efficiently by first estimating the power-of-10 exponent from the
power-of-2 exponent in the floating-point representation.

Code size is reduced by roughly 100 to 200 bytes by this commit.

Signed-off-by: Dan Ellis <dan.ellis@gmail.com>
This commit is contained in:
Dan Ellis
2022-07-28 10:49:18 -04:00
committed by Damien George
parent 6cd2e41918
commit 6f4d424f46
5 changed files with 53 additions and 97 deletions
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py/misc.h
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@@ -243,10 +243,12 @@ extern mp_uint_t mp_verbose_flag;
#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_DOUBLE
#define MP_FLOAT_EXP_BITS (11)
#define MP_FLOAT_EXP_OFFSET (1023)
#define MP_FLOAT_FRAC_BITS (52)
typedef uint64_t mp_float_uint_t;
#elif MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
#define MP_FLOAT_EXP_BITS (8)
#define MP_FLOAT_EXP_OFFSET (127)
#define MP_FLOAT_FRAC_BITS (23)
typedef uint32_t mp_float_uint_t;
#endif