Rif Rosh HaShana 7a {Rosh haShana 27b continues; 28a}

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7a

{Rosh haShana 27b continues}
{see Bach's addition here}
If it was split along its length, it is invalid. Along its width {all around its circumference}, if there is left enough to made a tekiah it is valid, and if not, it is invalid.
And how much is enough to make a tekiah?
Rabban Gamliel explained: enough that he holds it in his hand and it is visible here and there {along its length}.

If its sound was thin, thick, or harsh, it is valid, for all sounds are valid for shofar.

They sent to the father of Shmuel: If they bored a hole in its zichrus {that is, a bone goes out of the animal and into the shofar. Usually, they remove it, but here they left the bone and just bored a hole in it}, it is valid, for something of its own kind does not constitute a separation.

Mishna:
If one blew {the shofar} into a pit, into a cistern, or into a vat, if the sound of the shofar is heard, he has fulfilled. But if he heard an indistinct sound {alternatively: of reverberation/ an echo}, he did not fulfill.

If he was passing behind the synagogue or if his house was close to the synagogue, and he heard the sound of the shofar or the sound of the megillah -- if he directed his heart {with intent to fulfill the mitzvah; or perhaps in order to pay proper attention (and that it is not the sound of a donkey), see Ran's comment, and the implication of the continuation in the gemara as cited by Rif is the former} he fulfilled, and if not, he did not fulfill. And even though this one heard and this one heard, this one who directed his heart fulfilled and this one did not direct his heart and did not fufill.

Gemara:
Rav Huna said: They only learned this about those standing at the edge of the pit {on the outside, while he blew into the pit}, but those standing inside the pit fulfilled.

{Rosh haShana 28a}
Rav Yehuda said: With a shofar of idolatry, one should not blow, and if he blew, he fulfilled, for commandments are not given for {our} benefit.