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fix: normalize sign when imuln multiplies by zero - #321
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Multiplying a negative number by the plain number 0 zeroed the words but left the negative flag set, producing a negative zero. That value reported isNeg() as true, was not eq() to zero, compared as less than zero, and printed as -0. Clear the sign along with the length when the factor is zero so the result is a plain zero.
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* fix: correct divRound rounding for negative operands divRound computed the half-way threshold and the round-up direction from the raw operands, which only works when both are positive. With a negative dividend or divisor it compared a signed remainder against a value derived from the signed divisor, rounded in the wrong direction, and lost the sign when the truncated quotient was zero. Compare the magnitude of the remainder against half of the absolute divisor and step the quotient away from zero using the sign of the result, so rounding matches the positive case for every sign. * fix: normalize sign when imuln multiplies by zero (#321) * fix: normalize sign when imuln multiplies by zero Multiplying a negative number by the plain number 0 zeroed the words but left the negative flag set, producing a negative zero. That value reported isNeg() as true, was not eq() to zero, compared as less than zero, and printed as -0. Clear the sign along with the length when the factor is zero so the result is a plain zero. * use _normSign() --------- Co-authored-by: Kirill Fomichev <fanatid@ya.ru> * add more tests --------- Co-authored-by: Kirill Fomichev <fanatid@ya.ru>
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* fix: normalize sign when imuln multiplies by zero Multiplying a negative number by the plain number 0 zeroed the words but left the negative flag set, producing a negative zero. That value reported isNeg() as true, was not eq() to zero, compared as less than zero, and printed as -0. Clear the sign along with the length when the factor is zero so the result is a plain zero. * use _normSign() --------- Co-authored-by: Kirill Fomichev <fanatid@ya.ru> (cherry picked from commit dd84df8)
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* fix: correct divRound rounding for negative operands divRound computed the half-way threshold and the round-up direction from the raw operands, which only works when both are positive. With a negative dividend or divisor it compared a signed remainder against a value derived from the signed divisor, rounded in the wrong direction, and lost the sign when the truncated quotient was zero. Compare the magnitude of the remainder against half of the absolute divisor and step the quotient away from zero using the sign of the result, so rounding matches the positive case for every sign. * fix: normalize sign when imuln multiplies by zero (#321) * fix: normalize sign when imuln multiplies by zero Multiplying a negative number by the plain number 0 zeroed the words but left the negative flag set, producing a negative zero. That value reported isNeg() as true, was not eq() to zero, compared as less than zero, and printed as -0. Clear the sign along with the length when the factor is zero so the result is a plain zero. * use _normSign() --------- Co-authored-by: Kirill Fomichev <fanatid@ya.ru> * add more tests --------- Co-authored-by: Kirill Fomichev <fanatid@ya.ru> (cherry picked from commit 73fb9a4)
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Multiplying a negative number by the plain number 0 zeroed the words but left the negative flag set, producing a negative zero. That value reported
isNeg()as true, was noteq()to zero, compared as less than zero, and printed as-0.new BN(-5).mul(new BN(0))correctly gives0; only theimuln/mulnpath diverged.This clears the sign along with the length when the factor is zero so the result is a plain zero. The existing zero-multiplication test only checked
isZero(), which is true even for a negative zero, so the added test asserts the sign directly.