(cherry picked from commit bfd05d96)

(cherry picked from commit fc01c51c)

(cherry picked from commit f55d2716)

(cherry picked from commit d57593c1)

(cherry picked from commit 7c47ac71)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* add contract and tests

* avoid implicit cast

* add test cases

* fix test names

* modify avarage and add tests

* improve signed average formula

* fix lint

* better average formula

* refactor signed average testing

* add doc and changelog entry

* Update contracts/utils/math/SignedMath.sol

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* remove ceilDiv

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* add feature request #3084

* Update contracts/token/ERC20/ERC20.sol

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* Add changelog note

* add documentation

* test unlimitted allowance and add ERC777 unlimitted allowance

* reference PR in changelog

* documentation IERC20 -> ERC20

* use asciidoc note syntax

* use asciidoc note syntax

* typo

* typos

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* Name missing return variable in IERC721Enumerable

For consistency among all functions.

* remove return variable names

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

Correct a couple of misspellings.

* Reduce ERC20 allowance before triggering transfer

* adapt ERC777 to reduce allowance before transfer

* fix test for ERC777

* use smaller number to reduce balance

* simplify test description

* don't use deprecated expectEvents.inLogs

* fix test

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

* Add Base64 library to utils

* Fix typo on Base64 padding

* Added documentation for Base64 and references from ERC1155 and ERC721

* Updated Changelog

* Fix typo in utilities doc

* use mstore8 to improve memory accesses

* use shorter strings with encodePacked

* do not use using-for syntax, for clarity

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

* Avoid assembly in signature V and S decomposition

* Update ECDSA.sol

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Shelly Grossman <shelly@certora.com>
Co-authored-by: Aleksander Kryukov <58052996+RedLikeRosesss@users.noreply.github.com>
Co-authored-by: Michael M <91594326+MichaelMorami@users.noreply.github.com>
Co-authored-by: Aleksander Kryukov <firealexkryukov@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

Replace excodesize assembly with address.code.length (https://github.com/ethereum/solidity/releases/tag/v0.8.1) (#3025)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
Co-authored-by: Hadrien Croubois <hadrien@openzeppelin.com>