Resolve #81 to deal with a potential future scenario of PRNG generating 1
#120
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Hi @j0pgrm, re ulid#81 Your `if` statement is there to cover the possbility that your PRNG will generate the number 1. In general, PRNGs produce values from 0 to _less than_ 1, i.e. from the range 0 (inclusive) to 1 (exclusive). This is because when they generate an N-bit binary fraction, the highest value (all `1`s) will be just a tiny bit smaller than 1. Your `Math.floor` correctly rounds downward, so that `rand` will be in the range 0 (inclusive) to ENCODING_LEN *- 1* (inclusive). So the `if` will never be triggered. If, for some reason, you in future switch to a prng that somehow can generate a 1, for example because it has an idiosyncratic desire to cover a range of 0 (_exclusive_) to 1 (_inclusive_), then: * the chance of this is extremely small (1 in 2**N, not 1 in 2**8) * the PRNG will have lost the ability to generate 0 * your random character generator would have a micrscopically smaller chance of generating the first encoding character, and have a microscopic chance of trying to pick the non-existent character at #ENCODING_LEN. A neat solution for you is to simply wrap round that exactly-1 PRNG value back to 0, most conveniently A simple way to achieve this is to modulo the `rand` by ENCODING_LEN. Thank you for an excellent library.
darrelfrancis
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Hi @darrelfrancis! Apologies for not getting to this sooner. Your logic makes sense and the PR looks good imo, but I'd like the tests to run before considering a merge. For some reason they haven't run - I'll try to check that first, and simply run manually in your PR if I can't figure it out. |
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Hi @j0pgrm, re #81
Your
ifstatement is there to cover the possbility that your PRNG will generate the number 1. In general, PRNGs produce values from 0 to less than 1, i.e. from the range 0 (inclusive) to 1 (exclusive). This is because when they generate an N-bit binary fraction, the highest value (all1s) will be just a tiny bit smaller than 1.Your
Math.floorcorrectly rounds downward, so thatrandwill be in the range 0 (inclusive) to ENCODING_LEN - 1 (inclusive). So theifis never triggered.If, for some reason, you in future switch to a prng that somehow can generate a 1, for example because it has an idiosyncratic desire to cover a range of 0 (exclusive) to 1 (inclusive), then:
A neat solution for you is to simply wrap round that exactly-1 PRNG value back to 0. A simple way to achieve this is to modulo the
randby ENCODING_LEN.Thank you for an excellent library.