For the source text click/tap here: Yoma 17
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The Kohen Gadol receives one of the two loaves that are brought on Shavu'ot and four or five of the loaves of shewbread that is distributed weekly from the shulhan. Rabbi Yehuda HaNasi's position is that he always gets five, since he deserves half of the ten loaves that are distributed, based on the passage: Lev 29...
וְהָיְתָה לְאַהֲרֹן וּלְבָנָיו, וַאֲכָלֻהוּ בְּמָקוֹם קָדֹשׁ: כִּי קֹדֶשׁ קָדָשִׁים הוּא לוֹ, מֵאִשֵּׁי יְהוָה--חָק-עוֹלָם.
The Rashash points out that there is support for the idea that the Kohen Gadol received five loaves of the lehem ha-panim from the story related in Sefer Shmuel (21:4) when David is running away from King Sha'ul, and arrives in Nov, the city of kohanim.
David must rely on his wits (that is, falsely represent himself to the priest at Nob) in order to obtain needed food and weapons.