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Better document constraints on addcy carries (#1139)

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* Add missing constraints on addcy carries.

* Remove bit-checks; make documentation clearer.
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Hamish Ivey-Law 2023-08-01 20:58:32 +10:00 committed by GitHub
parent d8e314bc5c
commit 9e0719e6be
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1 changed files with 4 additions and 3 deletions
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7
evm/src/arithmetic/addcy.rs
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@ -68,13 +68,14 @@ const GOLDILOCKS_INVERSE_65536: u64 = 18446462594437939201;
/// Constrains x + y == z + cy*2^256, assuming filter != 0.
///
/// NB: This function DOES NOT verify that cy is 0 or 1; the caller
/// must do that.
///
/// Set `is_two_row_op=true` to allow the code to be called from the
/// two-row `modular` code (for checking that the modular output is
/// reduced).
///
/// NB: This function ONLY verifies that cy is 0 or 1 when
/// is_two_row_op=false; when is_two_row_op=true the caller must
/// verify for itself.
///
/// Note that the digits of `x + y` are in `[0, 2*(2^16-1)]`
/// (i.e. they are the sums of two 16-bit numbers), whereas the digits
/// of `z` can only be in `[0, 2^16-1]`. In the function we check that: