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py/modbuiltins: For round() builtin use nearbyint instead of round.
The C nearbyint function has exactly the semantics that Python's round() requires, whereas C's round() requires extra steps to handle rounding of numbers half way between integers. So using nearbyint reduces code size and potentially eliminates any source of errors in the handling of half-way numbers. Also, bare-metal implementations of nearbyint can be more efficient than round, so further code size is saved (and efficiency improved). nearbyint is provided in the C99 standard so it should be available on all supported platforms.
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4 files changed

Lines changed: 5 additions & 12 deletions

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‎esp8266/Makefile‎

Lines changed: 1 addition & 1 deletion
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@@ -108,7 +108,7 @@ LIB_SRC_C = $(addprefix lib/,\
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libc/string0.c \
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libm/math.c \
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libm/fmodf.c \
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libm/roundf.c \
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libm/nearbyintf.c \
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libm/ef_sqrt.c \
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libm/kf_rem_pio2.c \
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libm/kf_sin.c \

‎py/modbuiltins.c‎

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@@ -473,18 +473,11 @@ STATIC mp_obj_t mp_builtin_round(size_t n_args, const mp_obj_t *args) {
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mp_float_t val = mp_obj_get_float(o_in);
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mp_float_t mult = MICROPY_FLOAT_C_FUN(pow)(10, num_dig);
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// TODO may lead to overflow
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mp_float_t rounded = MICROPY_FLOAT_C_FUN(round)(val * mult) / mult;
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mp_float_t rounded = MICROPY_FLOAT_C_FUN(nearbyint)(val * mult) / mult;
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return mp_obj_new_float(rounded);
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}
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mp_float_t val = mp_obj_get_float(o_in);
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mp_float_t rounded = MICROPY_FLOAT_C_FUN(round)(val);
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mp_int_t r = rounded;
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// make rounded value even if it was halfway between ints
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if (val - rounded == 0.5) {
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r = (r + 1) & (~1);
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} else if (val - rounded == -0.5) {
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r &= ~1;
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}
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mp_float_t rounded = MICROPY_FLOAT_C_FUN(nearbyint)(val);
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#else
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mp_int_t r = mp_obj_get_int(o_in);
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#endif

‎qemu-arm/Makefile‎

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@@ -47,7 +47,7 @@ SRC_TEST_C = \
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LIB_SRC_C = $(addprefix lib/,\
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libm/math.c \
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libm/fmodf.c \
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libm/roundf.c \
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libm/nearbyintf.c \
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libm/ef_sqrt.c \
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libm/kf_rem_pio2.c \
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libm/kf_sin.c \

‎stmhal/Makefile‎

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@@ -86,7 +86,7 @@ SRC_LIB = $(addprefix lib/,\
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libm/atanf.c \
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libm/atan2f.c \
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libm/fmodf.c \
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libm/roundf.c \
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libm/nearbyintf.c \
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libm/log1pf.c \
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libm/acoshf.c \
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libm/asinhf.c \

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