Use |size_t| for array indexes. Use |int| for boolean flags. Declare
the variables that had their types changed closer to where they are
used.
Previously, some `for` loops depended on `i` being signed, so their
structure had to be changed to work with the unsigned type.
Change-Id: I247e4f04468419466733b6818d81d28666da0ad3
Reviewed-on: https://boringssl-review.googlesource.com/7468
Reviewed-by: David Benjamin <davidben@google.com>
afd6d9d61a