tree a81e450764c53106dac871ead992d0ee36c62534
parent ee78b6e6423a080cad320252030d0f7f002614f6
author Gilles Peskine <Gilles.Peskine@arm.com> 1668027736 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> 1668089725 +0100

Fix negative zero created by (-A) + (+A) or (-A) - (-A)

In mbedtls_mpi_add_mpi() and mbedtls_mpi_sub_mpi(), and by extention
mbedtls_mpi_add_int() and mbedtls_mpi_sub_int(), when the resulting value
was zero, the sign bit of the result was incorrectly set to -1 when the
left-hand operand was negative. This is not a valid mbedtls_mpi
representation. Fix this: always set the sign to +1 when the result is 0.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>