Topic: How many bytes stack size needed for FAST_MATH
Hello,
I wonder how many bytes of stack is needed to enable fast math?
Thanks.
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ReferenceswolfSSL - Embedded SSL Library → wolfSSL → How many bytes stack size needed for FAST_MATH
Hello,
I wonder how many bytes of stack is needed to enable fast math?
Thanks.
Hi burakkirazli,
It depends on the algorithms enabled/used and the FP_MAX_BITS you have defined. The ECC and RSA algorithms use fast math.
Typically during a TLS connection you'll have several of these on the stack. I recommend starting with 10KB of stack and then looking at your stack high watermark to determine how much to reduce.
For RSA the FP_MAX_BITS is double the maximum key size. For RSA 2048-bit requires double max bits so 4096. If you have just ECC defined than FP_MAX_BITS can be ECC max key size + 32. For both RSA and ECC you can reduce ECC stack usage by defining ALT_ECC_SIZE, which will use heap for the ECC point instead of stack.
We have some good examples for configuration the math library cases here:
https://github.com/wolfSSL/wolfssl/blob … settings.h
Thanks,
David Garske, wolfSSL
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