The functions in the presented code describe algorithms for conversions over numbers in binary form.
The s_block function performs a direct conversion using the s_table table. The input value input is an 8-bit number. The function defines row and column values that correspond to specific bits of the input value. These values are then used to retrieve an element from the s_table table using the formula (row * 4 + column) as usize. The result of the conversion is returned as the output value of the function.
The function s_block_inverse performs an inverse conversion using the table s_table_inverse. The conversion process is similar to s_block, but uses the s_table_inverse table. The input value input is converted to the corresponding element from the s_table_inverse table, and the result is returned as the output value.
The p_block function implements a bit rearrangement of the input value using the permutation_table table. The loop iterates through the values of the permutation_table table. For each value, the input number is shifted a certain number of positions to the right and then the last bit is extracted using a bitwise "AND" operation with 1. The resulting bit is written to position i in the output number. When the cycle is complete, the result is returned as the output value of the function.
These functions can be used in encryption and decryption algorithms to perform conversions on data in binary form, thus ensuring information confidentiality.