I saw different versions for the perfective ones.
Masculine past forms ending in -л, remove the - л and add -в(-вши) (the ending -вши is obsolete)
Masculine past forms ending in other consonants, add -ши.
Verbs ending in -ся have -вшись.
For infinitives ending in -йти, change -йти into -шедши.
Infinitive ending in -сти and masculine past forms ending in -ёл retain the -д and -т of the stem, e.g. привести - привед-ут > приведши e.g. подмести - подмут-ут > подметши
Verbs ending in -сти, -йти have another way of forming verbal adverbs: remove the 3rd personal plural ending and add -я: принести - принесут > принеся прийти - придут > придя найти - найдут > найдя
Some other verb endings are also like this: прочесть - прочт-ут > прочтя учесть - учт-ут > учтя ошибиться - ошиб-ятся > ошиобясь
- Some other verbs have two forms of verbal adverbs: принести - принёсши / принеся прообрести - приобрестши / приобрестя запереть - заперши / заперев ...... (the -а/-я ending is obsolete)
I'm quite confused about the rules for forming the perfective verbal adverbs. The basic rules should be 1, 2, 3 stated above, but the exceptions are complicated. It looks like -йти, -сти, -зти verbs have two forms of verbal adverbs. But it looks like some like прочесть must end in -я. The books don't seem to have been able to present the rules straightforwardly or simply enough. So what in fact are the rules?
This question was posed a few years ago by another individual, yet the responses provided at that time fell short in terms of being both helpful and insightful. Therefore, I feel the need to revisit this topic and ask here again.