Auto merge of #130002 - orlp:better-div-floor-ceil, r=thomcc · qinheping/verify-rust-std@4caabcd (original) (raw)

`@@ -3023,8 +3023,16 @@ macro_rules! int_impl {

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`pub const fn div_floor(self, rhs: Self) -> Self {

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`let d = self / rhs;

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`let r = self % rhs;

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``

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if (r > 0 && rhs < 0) || (r < 0 && rhs > 0) {

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``

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d - 1

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+

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// If the remainder is non-zero, we need to subtract one if the

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// signs of self and rhs differ, as this means we rounded upwards

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// instead of downwards. We do this branchlessly by creating a mask

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// which is all-ones iff the signs differ, and 0 otherwise. Then by

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// adding this mask (which corresponds to the signed value -1), we

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// get our correction.

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let correction = (self ^ rhs) >> (Self::BITS - 1);

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if r != 0 {

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d + correction

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`} else {

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` d

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`}

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`@@ -3059,8 +3067,12 @@ macro_rules! int_impl {

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`pub const fn div_ceil(self, rhs: Self) -> Self {

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`let d = self / rhs;

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`let r = self % rhs;

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``

`-

if (r > 0 && rhs > 0) || (r < 0 && rhs < 0) {

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``

`-

d + 1

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// When remainder is non-zero we have a.div_ceil(b) == 1 + a.div_floor(b),

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// so we can re-use the algorithm from div_floor, just adding 1.

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let correction = 1 + ((self ^ rhs) >> (Self::BITS - 1));

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if r != 0 {

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d + correction

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`} else {

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` d

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`}

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