Simplify division-with-remainder calculations in crypto/bn/div.c.

Create a |bn_div_rem_words| that is used for double-word/single-word
divisions and division-with-remainder. Remove all implementations of
|bn_div_words| except for the implementation needed for 64-bit MSVC.
This allows more code to be shared across platforms and also removes
an instance of the dangerous pattern wherein the |div_asm| macro
modified a variable that wasn't passed as a parameter.

Also, document the limitations of the compiler-generated code for the
non-asm code paths more fully. Compilers indeed have not improved in
this respect.

Change-Id: I5a36a2edd7465de406d47d72dcd6bf3e63e5c232
Reviewed-by: David Benjamin <>
4 files changed
tree: bc9a3aeb729fd7e14a7faf75cfda1740bf97006e
  1. .clang-format
  2. .gitignore
  4. CMakeLists.txt
  11. codereview.settings
  12. crypto/
  13. decrepit/
  14. fuzz/
  15. include/
  16. ssl/
  17. tool/
  18. util/


BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.

Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.

Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.

BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.

Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.

There are other files in this directory which might be helpful: