Revisions to How to divide an unsigned 8-bit integer by 3 without divide or multiply instructions (or lookup tables)

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edited Dec 16, 2022 at 19:21

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uint8_t div3(uint8_t x) { uint8_t a = x - (x >> 2); x >>= 1; x = a - (x >> 3); x = a - (x >> 3); x = a - (x >> 3); return x >> 1; }

uint8_t div3(uint8_t x) { uint8_t a = x - (x >> 2); x >>= 1; x = a - (x >> 3); x = a - (x >> 3); x = a - (x >> 3); return x >> 1; }

uint8_t div3(uint8_t x) { uint8_t a = x - (x >> 2); x = a - (x >> 3); x = a - (x >> 3); x = a - (x >> 3); return x >> 1; }

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edited Dec 16, 2022 at 18:51

user1095108

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-- this one just approximates

uint8_t div3(uint8_t x) { uint8_t a = x - (x >> 2); x >>= 1; x = a - (x >> 3); x = a - (x >> 3); x = a - (x >> 3); return x >> 1; }

-- this one just approximates

uint8_t div3(uint8_t x) { uint8_t a = x - (x >> 2); x >>= 1; x = a - (x >> 3); x = a - (x >> 3); x = a - (x >> 3); return x >> 1; }

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edited Dec 16, 2022 at 17:25

user1095108

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--

uint8_t div3(uint8_t x) { uint8_t a = x; x >>= 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1) + 1) >> 1; return x >> 1; }

--

uint8_t div3(uint8_t x) { uint8_t a = x; x >>= 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1)) >> 1; x = (a + (x >> 1) + 1) >> 1; return x >> 1; }