Long multiplication: Difference between revisions

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=={{header|RPL}}==

To solve the task, we need to develop part of a BigInt library ~~which~~ to handle very long integers as strings. Addition has been optimized with a 10-digit batch size, but multiplication is long (and slow), as required.

To solve the task, we need to develop part of a BigInt library to handle very long integers as strings. Addition has been optimized with a 10-digit batch size, but multiplication is long (and slow), as required.

{| class="wikitable"

! RPL code

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≫ ≫ ‘MULbig’ STO

|

NoZero ''( "0..0xyz" →"xyz" ) ''

NoZero ''( "0..0xyz" → "xyz" ) ''

count leading zeros

keep the rest

ZeroFill ''( "xyz" n →"0..0xyz" ) ''

ZeroFill ''( "xyz" n → "0..0xyz" ) ''

Swap→Zero ''( a b →a b Δlength ) ''

Swap→Zero ''( a b → a b Δlength ) ''

swap a and b if length(a) < length(b)

return length difference

ADDbig ''( "a" "b" →"a+b" ) ''

ADDbig ''( "a" "b" → "a+b" ) ''

res = "" ; carry = 0

for j = length(a) downto 1 step 10

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if b > 1E10 then digits -= 1E10 ; carry = 1

convert digits to 10-char string with leading zeros

prepend carry and remove leading zeros

DigitMul ''( "a" d →"a*d" ) ''

DigitMul ''( "a" d → "a*d" ) ''

res = "" ; carry = 0

for j = length(a) downto 1

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carry = digit // 10

digit %= 10

prepend carry

MULbig ''( "a" "b" →"a*b" ) ''

MULbig ''( "a" "b" → "a*b" ) ''

sum = "0" ; for j = length(b) downto 1

tmp = a * b[j]

shift left tmp length(b)-j times, then add to sum

|}

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1: "340282366920938463463374607431768211456"

</pre>

=={{header|Ruby}}==