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Author	SHA1	Message	Date
Damien George	bd556b6996	py: Fix compiling and decoding of args at large arg positions. There were two issues with the existing code: 1. "1 << i" is computed as a 32-bit number so would overflow when executed on 64-bit machines (when mp_uint_t is 64-bit). This meant that args beyond 32 positions would not be handled correctly. 2. star_args must fit as a positive small int so that it is encoded correctly in the emitted code. MP_SMALL_INT_BITS is too big because it overflows a small int by 1 bit. MP_SMALL_INT_BITS - 1 does not work because it produces a signed small int which is then sign extended when extracted (even by mp_obj_get_int_truncated), and this sign extension means that any position arg after *args is also treated as a star-arg. So the maximum bit position is MP_SMALL_INT_BITS - 2. This means that MP_OBJ_SMALL_INT_VALUE() can be used instead of mp_obj_get_int_truncated() to get the value of star_args. These issues are fixed by this commit, and a test added. Signed-off-by: Damien George <damien@micropython.org>	3 years ago

Author

SHA1

Message

Date

Damien George

bd556b6996

py: Fix compiling and decoding of *args at large arg positions.

There were two issues with the existing code:

1. "1 << i" is computed as a 32-bit number so would overflow when
   executed on 64-bit machines (when mp_uint_t is 64-bit).  This meant that
   *args beyond 32 positions would not be handled correctly.

2. star_args must fit as a positive small int so that it is encoded
   correctly in the emitted code.  MP_SMALL_INT_BITS is too big because it
   overflows a small int by 1 bit.  MP_SMALL_INT_BITS - 1 does not work
   because it produces a signed small int which is then sign extended when
   extracted (even by mp_obj_get_int_truncated), and this sign extension
   means that any position arg after *args is also treated as a star-arg.
   So the maximum bit position is MP_SMALL_INT_BITS - 2.  This means that
   MP_OBJ_SMALL_INT_VALUE() can be used instead of
   mp_obj_get_int_truncated() to get the value of star_args.

These issues are fixed by this commit, and a test added.

Signed-off-by: Damien George <damien@micropython.org>

3 years ago

1 Commits (5d07d0c7b0b2b3601d69a74da837d77e65941f75)