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Print the modular multiplicative inverse / virtual fractions
  • ### Goal
  • Print the [modular multiplicative inverse](https://en.wikipedia.org/wiki/Modular_multiplicative_inverse) with a modulus of 65536 (or a higher exponent of 2) for odd numbers 1-97.
  • ### Example output
  • Print these values (or an extension of them):
  • ```
  • 1
  • 43691
  • 52429
  • 28087
  • 36409
  • 35747
  • 20165
  • 61167
  • 61681
  • 51739
  • 53053
  • 14247
  • 23593
  • 55827
  • 49717
  • 31711
  • 33761
  • 44939
  • 7085
  • 28567
  • 39961
  • 48771
  • 20389
  • 18127
  • 22737
  • 64251
  • 21021
  • 46471
  • 60937
  • 55539
  • 38677
  • 61375
  • 4033
  • 19563
  • 4749
  • 43383
  • 61945
  • 51555
  • 14469
  • 5807
  • 18609
  • 17371
  • 64765
  • 60263
  • 18409
  • 12243
  • 54261
  • 23455
  • 41889
  • ```
  • ### Rules
  • - Use a modulus of at least $65536 = 2^{16}$. But you can use any modulus $ M = 2^N$ for $N ≥ 16$ and $N \in \mathbb{N} $ .
  • - Print the modular multiplicative inverse for at least all the natural, odd values $<98$.
  • - You can print it in any normal base.
  • - You can print additional stuff, but it should be clear which parts belong to the modular multiplicative inverse and which do not.
  • - Your program should print the required output in less than 1 hour on a modern PC (or other hardware that is affordable).
  • ### Ungolfed example
  • ```
  • #!/usr/bin/env python3
  • # Calculates the modular multiplicative inverse
  • def imod(a, n):
  • c=1
  • while c % a:
  • c+=n
  • return c//a
  • # Print the multiplicative inverse for 16-bit integers
  • n=2**16
  • for i in range(1,98,2): #For the values 1/1, 1/3, ... 1/97
  • b = imod(i,n)
  • print("{:>2} * 0x{:>04X} = {:2>} mod 0x{:>04X}".format(i,b,i*b%n,n))
  • ```
  • -------
  • ### Why these numbers are interesting
  • You don't have to understand this part in order to participate in the challenge.
  • There are multiple ways to look at these numbers. All lead to the same numbers. I call them **virtual fractions** (made up term). Virtual fractions are integers that have the feature that you can multiply them with the denominator and you get the numerator when you store them in a N-Bit integer. This only works for odd denominators. You can even add and multiply virtual fractions and they behave like you would expect from real fractions (assuming you use enough bits).
  • For example, you have the 16 bit unsigned integer with the value `0xAAAB` (43691). You can multiply it with 3 and get 1.
  • ```
  • 3 * 0xAAAB = 3 * 0b1010 1010 1010 1011 = 3 * 43691
  • = 0x20001 = 0b10 0000 0000 0000 0001 = 131073
  • Storing it in a 16 bit variable drops the 1 at bit 17:
  • = 0x0001 = 0b0000 0000 0000 0001 = 1
  • ```
  • This does the following operation: $1 ≡ 3 \cdot 43691 \mod 65536$ (which would be `1%65536 == 43691%65536` or `1&0xFFFF == 43691&0xFFFF` in C). This is interesting because that is what a 16-Bit [ALU](https://en.wikipedia.org/wiki/Arithmetic_logic_unit) would do when it multiples `0xAAABu * 3u`.
  • Therefore, `0xAAAB` is like $1/3$.
  • There are other ways to look at these numbers, but that should be enough for this challenge.
  • ## Goal
  • Print the [modular multiplicative inverse](https://en.wikipedia.org/wiki/Modular_multiplicative_inverse) with a modulus of 65536 (or a higher exponent of 2) for odd numbers 1-97.
  • ## Example output
  • Print these values (or an extension of them):
  • ```
  • 1
  • 43691
  • 52429
  • 28087
  • 36409
  • 35747
  • 20165
  • 61167
  • 61681
  • 51739
  • 53053
  • 14247
  • 23593
  • 55827
  • 49717
  • 31711
  • 33761
  • 44939
  • 7085
  • 28567
  • 39961
  • 48771
  • 20389
  • 18127
  • 22737
  • 64251
  • 21021
  • 46471
  • 60937
  • 55539
  • 38677
  • 61375
  • 4033
  • 19563
  • 4749
  • 43383
  • 61945
  • 51555
  • 14469
  • 5807
  • 18609
  • 17371
  • 64765
  • 60263
  • 18409
  • 12243
  • 54261
  • 23455
  • 41889
  • ```
  • ## Rules
  • - Use a modulus of at least $65536 = 2^{16}$. But you can use any modulus $ M = 2^N$ for $N ≥ 16$ and $N \in \mathbb{N} $ .
  • - Print the modular multiplicative inverse for at least all the natural, odd values $<98$.
  • - You can print it in any normal base.
  • - You can print additional stuff, but it should be clear which parts belong to the modular multiplicative inverse and which do not.
  • - Your program should print the required output in less than 1 hour on a modern PC (or other hardware that is affordable).
  • ## Ungolfed example
  • ```
  • #!/usr/bin/env python3
  • # Calculates the modular multiplicative inverse
  • def imod(a, n):
  • c=1
  • while c % a:
  • c+=n
  • return c//a
  • # Print the multiplicative inverse for 16-bit integers
  • n=2**16
  • for i in range(1,98,2): #For the values 1/1, 1/3, ... 1/97
  • b = imod(i,n)
  • print("{:>2} * 0x{:>04X} = {:2>} mod 0x{:>04X}".format(i,b,i*b%n,n))
  • ```
  • -------
  • ## Why these numbers are interesting
  • You don't have to understand this part in order to participate in the challenge.
  • There are multiple ways to look at these numbers. All lead to the same numbers. I call them **virtual fractions** (made up term). Virtual fractions are integers that have the feature that you can multiply them with the denominator and you get the numerator when you store them in a N-Bit integer. This only works for odd denominators. You can even add and multiply virtual fractions and they behave like you would expect from real fractions (assuming you use enough bits).
  • ### Example for 1/3
  • For example, you have the 16 bit unsigned integer with the value `0xAAAB` (43691). You can multiply it with 3 and get 1.
  • ```
  • 3 * 0xAAAB = 3 * 0b1010 1010 1010 1011 = 3 * 43691
  • = 0x20001 = 0b10 0000 0000 0000 0001 = 131073
  • Storing it in a 16 bit variable drops the 1 at bit 17:
  • = 0x0001 = 0b0000 0000 0000 0001 = 1
  • ```
  • This does the following operation: $1 ≡ 3 \cdot 43691 \mod 65536$ (which would be `1%65536 == 43691%65536` or `1&0xFFFF == 43691&0xFFFF` in C). This is interesting because that is what a 16-Bit [ALU](https://en.wikipedia.org/wiki/Arithmetic_logic_unit) would do when it multiples `0xAAABu * 3u`.
  • Therefore, `0xAAAB` is like $1/3$.
  • There are other ways to look at these numbers, but that should be enough for this challenge.

Suggested 3 months ago by trichoplax‭