diff options
| author | Jeff Epler <jepler@gmail.com> | 2025-07-23 16:14:22 -0500 |
|---|---|---|
| committer | Damien George <damien@micropython.org> | 2025-10-01 09:23:05 +1000 |
| commit | a80913292153a14424b29bdb9ca8847e8d35cf73 (patch) | |
| tree | 9d073ab5c9c1773d30daa89d3062c3ee1bbed380 /py/mpconfig.h | |
| parent | 3dd8073c290c077f17ffdee17a019763ad82604d (diff) | |
py: Add MICROPY_USE_GCC_MUL_OVERFLOW_INTRINSIC.
Most MCUs apart from Cortex-M0 with Thumb 1 have an instruction
for computing the "high part" of a multiplication (e.g., the upper
32 bits of a 32x32 multiply).
When they do, gcc uses this to implement a small and fast
overflow check using the __builtin_mul_overflow intrinsic, which
is preferable to the guard division method previously used in smallint.c.
However, in contrast to the previous mp_small_int_mul_overflow
routine, which checks that the result fits not only within mp_int_t
but is SMALL_INT_FITS(), __builtin_mul_overflow only checks for
overflow of the C type. As a result, a slight change in the code
flow is needed for MP_BINARY_OP_MULTIPLY.
Other sites using mp_small_int_mul_overflow already had the
result value flow through to a SMALL_INT_FITS check so they didn't
need any additional changes.
Do similarly for the _ll and _ull multiply overflows checks.
Signed-off-by: Jeff Epler <jepler@gmail.com>
Diffstat (limited to 'py/mpconfig.h')
| -rw-r--r-- | py/mpconfig.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/py/mpconfig.h b/py/mpconfig.h index f4b7c1058..45178034a 100644 --- a/py/mpconfig.h +++ b/py/mpconfig.h @@ -2336,4 +2336,23 @@ typedef time_t mp_timestamp_t; #define MP_WARN_CAT(x) (NULL) #endif +// If true, use __builtin_mul_overflow (a gcc intrinsic supported by clang) for +// overflow checking when multiplying two small ints. Otherwise, use a portable +// algorithm. +// +// Most MCUs have a 32x32->64 bit multiply instruction, in which case the +// intrinsic is likely to be faster and generate smaller code. The main exception is +// cortex-m0 with __ARM_ARCH_ISA_THUMB == 1. +// +// The intrinsic is in GCC starting with version 5. +#ifndef MICROPY_USE_GCC_MUL_OVERFLOW_INTRINSIC +#if defined(__ARM_ARCH_ISA_THUMB) && (__GNUC__ >= 5) +#define MICROPY_USE_GCC_MUL_OVERFLOW_INTRINSIC (__ARM_ARCH_ISA_THUMB >= 2) +#elif (__GNUC__ >= 5) +#define MICROPY_USE_GCC_MUL_OVERFLOW_INTRINSIC (1) +#else +#define MICROPY_USE_GCC_MUL_OVERFLOW_INTRINSIC (0) +#endif +#endif + #endif // MICROPY_INCLUDED_PY_MPCONFIG_H |