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a7d440eaec
The array storing deltas between sequential prime numbers could be
compressed, as the vast majority of the values in the array does not
require more than 4 buts to store.
The new storage format is as follows:
- each differential value (difference between two consecutive primes)
is halved and stored in 4 bits, two halved values are packed per
byte.
- I the first one of of the two sequential halved values exceeds 0xf,
it is stored in the array followed by a zero, stored as is (without
halving), thus taking two bytes.
- if the second one of the two sequential halved values exceeds 0xf,
both values are stored in the array as is, both prepended by zeros,
thus taking 4 bytes.
The code calculating the sequential primes parses the array according
to this format. Storing the primes in this format allows to shave from
the image size 1848 bytes.
BRANCH=cr50
BUG=b:65253310, b:65287300
TEST=verified that test_rsa test from the tpmtest suite passes.
verified that the list of prime numbers printed out when
PRINT_PRIMES is defined and test_rsa is ran is the same before
and after this patch.
Change-Id: Ifdc2858a48f868ef816ccb4e351d9f60703d16e7
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/664253
Reviewed-by: Nagendra Modadugu <ngm@google.com>