| // Package midpoint encapsulates all logic pertaining to determining the next candidate for bisection. |
| // |
| // Bisection finds a culprit for some performance regression by continuously comparing two commits. |
| // The range of commits is reduced by half for every iteration, until one commit that causes a |
| // regression is identified. |
| // |
| // As part of that search, the next "candidate" to compare against is found by calculating the midpoint |
| // between two commits. Once all options have been exhausted (specifically, when the starting and |
| // ending commits are adjacent to each other), the system assumes a DEPS roll and searches for the |
| // culprit in the range of commits rolled in. |
| // |
| // For example, if we have C1 and C5: |
| // Gitiles Logs would return [C5, C4, C3, C2]. C5 is popped off, and we're left with |
| // [C4, C3, C2]. Because the ordering is from latest -> earliest, this is reversed, and |
| // thus becomes [C2, C3, C4]. The calculated midpoint would be at index 1, or C3. |
| // |
| // The next iterations would be as follows: C1 - C3 and C3 - C5. |
| // Gitiles Logs would return [C3, C2] and removing C3 leaves C2, which would be the next |
| // midpoint for that pair. Following the same logic, C4 would be the midpoint for C3 - C5. |
| // |
| // In the final iteration, we are left with adjacent pairs ie/ C1 - C2 // C2 - C3 ... |
| // It's assumed that there's been a DEPS roll between C1 and C2. DEPS file for each commit |
| // is unpacked. |
| // |
| // If there indeed was a DEPS roll, and thus the revision for a project (ie/ V8) has been rolled, |
| // the "dependency" field of the response will be non-nil, denoting the start, mid and end for the |
| // roll. |
| // |
| // For example, if between C1 and C2 there's a V8 roll, and if V8 is rolled from V1 to V3, |
| // the expected response would be: |
| // |
| // Commit { |
| // gitHash: C1, |
| // repoisitoryUrl: "https://chromium.org/chromium/src" |
| // dependency: Dependency { |
| // repositoryUrl: V8, |
| // startGitHash: V1, |
| // endGitHash: V3, |
| // midGitHash: V2, |
| // } |
| // } |
| package midpoint |
