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fix comment, ChangeLog & migration-guide for MBEDTLS_ECP_FIXED_POINT_OPTIM

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Signed-off-by: kXuan <kxuanobj@gmail.com>
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kXuan 2021-06-02 16:53:42 +08:00
parent 22fc906d57
commit 782c2b9f36
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3 changed files with 14 additions and 10 deletions
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6
ChangeLog.d/issue4128.txt
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@ -1,4 +1,4 @@
API changes
* The option `MBEDTLS_ECP_FIXED_POINT_OPTIM` use pre-computed comb tables
instead of computing tables in runtime. Thus, this option now use more
ROM, and it does not increase RAM usage in runtime anymore.
* The option MBEDTLS_ECP_FIXED_POINT_OPTIM use pre-computed comb tables
instead of computing tables in runtime. Thus, this option now increase
code size, and it does not increase RAM usage in runtime anymore.

11
docs/3.0-migration-guide.d/modify_MBEDTLS_ECP_FIXED_POINT_OPTIM_behaviour.md
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@ -1,8 +1,11 @@
Change MBEDTLS_ECP_FIXED_POINT_OPTIM behaviour
------------------------------------------------------
The option MBEDTLS_ECP_FIXED_POINT_OPTIM now use more ROM and does not increase
peak RAM usage anymore.
The option `MBEDTLS_ECP_FIXED_POINT_OPTIM` now increase code size and it does
not increase peak RAM usage anymore.
If you are limited by code size, you can define `MBEDTLS_ECP_FIXED_POINT_OPTIM`
to `0` in your config file. The impact depends on the number and size of
enabled curves. For example, for P-256 the difference is 1KB; see the documentation
of this option for details.
If you are limited by ROM space, you can define MBEDTLS_ECP_FIXED_POINT_OPTIM
to `0` in your config file. This will save about 50 KiB ROM space.

7
include/mbedtls/ecp.h
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@ -276,15 +276,16 @@ mbedtls_ecp_group;
#if !defined(MBEDTLS_ECP_FIXED_POINT_OPTIM)
/*
* Trade ROM usage for speed on fixed-point multiplication.
* Trade code size for speed on fixed-point multiplication.
*
* This speeds up repeated multiplication of the generator (that is, the
* multiplication in ECDSA signatures, and half of the multiplications in
* ECDSA verification and ECDHE) by a factor roughly 3 to 4.
*
* The cost is increasing ROM usage by a factor roughly 2.
* For each n-bit Short Weierstrass curve that is enabled, this adds 4n bytes
* of code size if n < 384 and 8n otherwise.
*
* Change this value to 0 to reduce ROM usage.
* Change this value to 0 to reduce code size.
*/
#define MBEDTLS_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up. */
#endif /* MBEDTLS_ECP_FIXED_POINT_OPTIM */