fix(tw/ubn): accept 2023 relaxed check-digit rule (divisible by 5)#1
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fix(tw/ubn): accept 2023 relaxed check-digit rule (divisible by 5)#1gccbb02498 wants to merge 1 commit into
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Effective 2023-04-01, Taiwan's Ministry of Finance changed the Unified Business Number (統一編號) check-digit logic so the weighted digit sum only needs to be divisible by 5 (previously 10), expanding the number space while keeping the same 8-digit format. Every old, divisible-by-10 number is still divisible by 5, so existing numbers remain valid. - Relax the checksum from `sum % 10 === 0` to `sum % 5 === 0`. - Keep the 7th-digit-is-7 special case (7*4=28 sums to 10), now checked against the mod-5 remainder. - Add tests: an old-rule number (04595257), a new divisible-by-5 number (00501508), and a new 7th-digit special case (00000074). Ref: https://www.fia.gov.tw/singlehtml/3?cntId=c4d9cff38c8642ef8872774ee9987283 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Superseded by upstream PR koblas#159 — contributing the fix directly to the upstream project. |
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Problem
The Taiwan Unified Business Number (統一編號 / UBN) validator still uses the old rule where the weighted digit sum must be divisible by 10. Effective 2023-04-01, Taiwan's Ministry of Finance relaxed the check-digit logic from "divisible by 10" to "divisible by 5" to expand the number space. The format is unchanged, and every old (divisible-by-10) number is also divisible by 5, so the change is fully backward compatible.
As a result, the current implementation incorrectly rejects legitimate UBNs issued after 2023 (those that are only divisible by 5) as
InvalidChecksum.Fix
sum % 10 === 0tosum % 5 === 0.7(7 * 4 = 28, whose digit sum is 10 and may be counted as either 1 or 0), now evaluated against the mod-5 remainder.Tests
0459525700501503005015080000007400501502jest src/tw/ubn.spec.ts→ 7 passed. lint and tsc both pass.Reference
https://www.fia.gov.tw/singlehtml/3?cntId=c4d9cff38c8642ef8872774ee9987283
🤖 Generated with Claude Code