Fix bpe_gpt2_preprocess

[bobqianic]

This is a byproduct of the work on whisper.cpp. Could anyone conduct a few tests to verify if it resolves the issue detailed at #3502? @ggerganov

In the development of whisper.cpp, I've performed tests on a relatively large dataset, and the results have been quite promising. You can find more details about this testing at ggml-org/whisper.cpp#1854.

[ggerganov]

There is a tokenization test that is failing with this change:

make -j tests && ./tests/test-tokenizer-0-falcon ./models/ggml-vocab-falcon.gguf

...
src: '
 ='
res: '
 ='
tok: 193 204 40 
main : failed test:    '
 ='
main : detokenized to: '
 =' instead of '
 ='
main : expected tokens:   1212,     40, 
main : got tokens:         193,    204,     40, 

I.e. the string \n = used to tokenize to [1212, 40] and now it tokenizes to [193, 204, 40]. Can you confirm which is correct?

[bobqianic]

It's odd, but this PR seems to undo the bug fix introduced in PR #3567, which aimed to address the issue reported in Issue #3502.

I'll check if reverting to the version before PR #3567 eliminates the error encountered in whisper.cpp

Edit: After rolling back to the version prior to PR #3567, the situation become even worse. The error rate surged to 0.507%

[bobqianic]

We might need to add some additional code to ensure our tokenizer aligns with the Falcon tokenizer's behavior. It seems there aren't any major issues with this pull request. Echoing @apage43's comments in this discussion, to match the Falcon tokenizer exactly, we should consider developing specific functions aimed at this requirement, rather than altering the bpe_gpt2_preprocess function. @ggerganov

[bobqianic]

This time, I will conduct some stricter tests, using a test set that is 50 times larger than the previous one, wikitext1 (500MiB), as the test set, and compare it with OpenAI's tokenizer to ensure the correctness of bpe_gpt2_preprocess.

Edit: Great news. No errors were detected!

[ggerganov]

Ok, got it. We should however fix the test - maybe just use the new set of tokens and add a short comment explaining why there is a difference (or just link to this discussion)

[ggerganov]

Btw, #5464 claims to fix some issues in the BPE preprocess function - might be useful

[bobqianic]

Btw, #5464 claims to fix some issues in the BPE preprocess function - might be useful

I attempted to build the PR you mentioned, but unfortunately, it didn't succeed.

C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(415): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(415): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(419): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(419): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(444): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(444): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(448): error C2015: too many characters in constant
C:\Users\qianp\CLionProjects\testcpp\unicode_v2.h(448): error C2015: too many characters in constant

[bobqianic]

Good, nearly all of Falcon's tokenizer tests have failed, which indicates that our implementation of bpe_gpt2_preprocess is correct.