Using Neon for float to int conversion, and introducing platform-
specific function for converting an array of float values to int16.
Also adding appropriate unit test.

Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>

Prevents integer overflow UB in the shift rounding when the signal blows
up on bad bitstreams (if it triggers, the signal was already unusable
anyway).

Not really a problem in practice (the packet is broken anyway)
but caught by asan.

Could only happen on 32-bit fixed-point builds.
The bug was introduced in 4ba06d9e.

Silences -fsanitize=unsigned-integer-overflow even though the code was
valid (not undefined) C.

Silences -fsanitize=unsigned-integer-overflow even though the code was
valid (not undefined) C.

Change-Id: Ib016fc8f0066980e3e5122b3f286680adc228ff9
Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>

The exp2 function was approximated using lolremez, achieving an
accuracy of less than 2*10^-7 within the range of 0 to 1.

Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>

Change-Id: Ibd0d16918272cb568923d384475e139dc312c61b
Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>

The log2 function was approximated using lolremez, achieving an
accuracy of less than 1.4*10^-8 within the range of 1 to 2.

Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>

Convert to 16 bits only at the very end