fix: get_next_power_exponent off by 1 #11169
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benesjan
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benesjan
commented
Jan 10, 2025
| @@ -20,7 +20,8 @@ pub struct VariableMerkleTree { | |||
| /// The smallest exponent `n` where `2^n >= input` | |||
| unconstrained fn get_next_power_exponent(input: u32, start: u8) -> u8 { | |||
| let mut next_power_exponent = 0; | |||
| if input <= 2 << start { | |||
| // We check if input is less than or equal to 2^start. | |||
| if input <= (1 << start) { | |||
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This was a crux of the bug because 2 << start is not equal to 2^start but to 2^(start+1).
benesjan
commented
Jan 10, 2025
| @@ -49,8 +50,8 @@ fn get_prev_power_2(value: u32) -> u32 { | |||
| get_next_power_exponent(value, 0) | |||
| }; | |||
|
|
|||
| let next_power_2 = 2 << next_power_exponent; | |||
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Here it didn't cause an issue because we were shifting 2 and not 1.
benesjan
commented
Jan 10, 2025
| let next_power_2 = 2 << next_power_exponent; | ||
| let prev_power_2 = next_power_2 / 2; | ||
| let prev_power_2 = 1 << (next_power_exponent - 1); | ||
| let next_power_2 = prev_power_2 * 2; |
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I sneaked in an optimization. I compute prev_power_2 first and then I multiply by 2 to get next_power_2. This should be cheaper constraint-wise as division is more expensive than multiplication.
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MirandaWood
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Jan 13, 2025
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This reverts commit 06e9cc2.
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* master: (329 commits) fix(avm): mac build (#11195) fix: docs rebuild patterns (#11191) chore: refactor Solidity Transcript and improve error handling in sol_honk flow (#11158) chore: move witness computation into class plus some other cleanup (#11140) fix: get_next_power_exponent off by 1 (#11169) chore(avm): vm2 followup cleanup (#11186) fix: underconstrained bug (#11174) refactor: VariableMerkleTree readability improvements (#11165) chore: removing noir bug workaround (#10535) chore(docs): Remove node pages (#11161) git subrepo push --branch=master noir-projects/aztec-nr git_subrepo.sh: Fix parent in .gitrepo file. [skip ci] chore: replace relative paths to noir-protocol-circuits git subrepo push --branch=master barretenberg feat(avm2): avm redesign init (#10906) feat: Sync from noir (#11138) feat: simulator split (#11144) chore: rpc server cleanup & misc fixes (#11145) git subrepo push --branch=master noir-projects/aztec-nr git_subrepo.sh: Fix parent in .gitrepo file. [skip ci] ...
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There was an issue with
get_next_power_exponentfunc which resulted in it returning values off by 1. This didn't cause a bug but it was confusing.