Laboratory 6 - Exercises

Instructions working on strings of bytes/words/doublewords/quadwords

Exercises

The following exercises need to be solved using specific string instructions: LODSB, STOSB, MOVSB, SCASB, CMPSB, LODSW, STOSW, MOVSW, SCASW, CMPSW, LODSD, STOSD, MOVSD, SCASD, CMPSD.
  1.  An array with doublewords containing packed data (4 bytes written as a single doubleword) is given. Write an asm program in order to obtain a new array of doublewords, where each doubleword will be composed by the rule: the sum of the bytes from an odd position will be written on the word from the odd position and the sum of the bytes from an even position will be written on the word from the even position. The bytes are considered to represent signed numbers, thus the extension of the sum on a word will be performed according to the signed arithmetic.

    Example:

    for the initial array: 
    127F5678h, 0ABCDABCDh, ...
    The following should be obtained: 
    006800F7h, 0FF56FF9Ah, ...
  2. An array of words is given. Write an asm program in order to obtain an array of doublewords, where each doubleword will contain each nibble unpacked on a byte (each nibble will be preceded by a 0 digit), arranged in an ascending order within the doubleword.

    Example:

    for the initial array: 
    1432h, 8675h, 0ADBCh, ...
    The following should be obtained: 
    01020304h, 05060708h, 0A0B0C0Dh, ...
  3. An array of doublewords, where each doubleword contains 2 values on a word (unpacked, so each nibble is preceded by a 0) is given. Write an asm program to create a new array of bytes which contain those values (packed on a single byte), arranged in an ascending manner in memory, these being considered signed numbers.

    Example:

    for the initial array: 
    0702090Ah, 0B0C0304h, 05060108h
    the following should be obtained: 
    72h, 9Ah, 0BCh, 34h, 56h, 18h
    which arranged in an ascending manner will give: 
    9Ah, 0BCh, 18h, 34h, 56h, 72h
  4. A byte string s is given. Build the byte string d such that every byte d[i] is equal to the count of ones in the corresponding byte s[i] of s.

    Example:

    s: 5, 25, 55, 127
    in binary: 
    101, 11001, 110111, 1111111
    d: 2, 3, 5, 7
  5. Two byte strings s1 and s2 are given. Build the byte string d such that, for every byte s2[i] in s2, d[i] contains either the position of byte s2[i] in s1, either the value of 0.

    Example:

    pos:1 2 3 4 5
    s1: 7, 33, 55, 19, 46
    s2: 33, 21, 7, 13, 27, 19, 55, 1, 46 
    d: 2,  0, 1, 0, 0, 4, 3, 0, 5
  6. A word string s is given. Build the byte string d such that each element d[i] contains:
    - the count of zeros in the word s[i], if s[i] is a negative number
    - the count of ones in the word s[i], if s[i] is a positive number

    Example:

    s: -22, 145, -48, 127
    in binary:
    1111111111101010, 10010001, 1111111111010000, 1111111
    d: 3, 3, 5, 7
  7. A string of doublewords is given. Obtain the list made out of the high bytes of the high words of each doubleword from the given list with the property that these bytes are multiple of 3.

    Example:

    Given the string of doublewords: 
    s DD 12345678h, 1A2B3C4Dh, FE98DC76h
    obtain the string of bytes: 
    d: 12h.
  8. A list of doublewords is given. Obtain the list made out of the low bytes of the high words of each doubleword from the given list with the property that these bytes are palindromes in base 10.

    Example:

    Given the string of doublewords:
    s DD 12345678h, 1A2C3C4Dh, 98FCDC76h
    obtain the string of bytes: 
    d DB 2Ch, FCh.
  9. A list of doublewords is given. Starting from the low part of the doubleword, obtain the doubleword made of the high even bytes of the low words of each doubleword from the given list. If there are not enough bytes, the remaining bytes of the doubleword will be filled with the byte FFh.

    Example:

    Given the string of doublewords: 
     s DD 12345678h, 1A2C3C4Dh, 98FCDD76h, 12783A2Bh
    obtain the doubleword: 
    d DD FF3A3C56h
    .
  10. Given an array A of words, build two arrays of bytes:  
     - array B1 contains as elements the higher part of the words from A
     - array B2 contains as elements the lower part of the words from A
  11. Given an array A of doublewords, build two arrays of bytes:  
     - array B1 contains as elements the higher part of the higher words from A
     - array B2 contains as elements the lower part of the lower words from A
  12. Given an array A of doublewords, build two arrays of bytes:  
     - array B1 contains as elements the lower part of the lower words from A
     - array B2 contains as elements the higher part of the higher words from A
  13. Given an array S of doublewords, build the array of bytes D formed from lower bytes of lower words, bytes multiple of 7.

    Example:

     s DD 12345607h, 1A2B3C15h, 13A33412h
     d DB 07h, 15h
  14. Given an array S of doublewords, build the array of bytes D formed from bytes of doublewords sorted as unsigned numbers in ascending order.

    Example:

     s DD 12345607h, 1A2B3C15h
     d DB 07h, 12h, 15h, 1Ah, 2Bh, 34h, 3Ch, 56h
  15. Given an array S of doublewords, build the array of bytes D formed from bytes of doublewords sorted as unsigned numbers in descending order.

    Example:

     s DD 12345607h, 1A2B3C15h
     d DB 56h, 3Ch, 34h, 2Bh, 1Ah, 15h, 12h, 07h
  16. Being given two alphabetical ordered strings of characters, s1 and s2, build using merge sort the ordered string of bytes that contain all characters from s1 and s2.
  17. A string of doublewords is given. Order in decreasing order the string of the low words (least significant) from these doublewords. The high words (most significant) remain unchanged.

    Example:

    being given 
    sir DD 12345678h 1256ABCDh, 12AB4344h
    the result will be 
    1234ABCDh, 12565678h, 12AB4344h.
  18. A string of doublewords is given. Order in increasing order the string of the high words (most significant) from these doublewords. The low words (least significant) remain unchanged.

    Example:

    being given 
    sir DD 12AB5678h, 1256ABCDh, 12344344h
    the result will be 
    12345678h, 1256ABCDh, 12AB4344h.
  19. Being given two strings of bytes, compute all positions where the second string appears as a substring in the first string.
  20. Being given a string of bytes representing a text (succession of words separated by spaces), determine which words are palindromes (meaning may be interpreted the same way in either forward or reverse direction); ex.: "cojoc", "capac" etc.
  21. Being given a string of words, obtain the string (of bytes) of the digits in base 10 of each word from this string.

    Example:

    being given the string 
    sir DW 12345, 20778, 4596
    the result will be 
    1, 2, 3, 4, 5, 2, 0, 7, 7, 8, 4, 5, 9, 6.
  22. A string of bytes 'input' is given together with two additional strings of N bytes each, 'src' and 'dst'. Obtain a new string of bytes called 'output' from the 'input' string, by replacing all the bytes with the value src[i] with the new value dst[i], for i=1..N.
  23. Being given a string of bytes, build a string of words which contains in the low bytes of the words the set of distinct characters from the given string and in the high byte of a word it contains the number of occurrences of the low byte of the word in the given byte string.

    Example:

    given the string 
    sir DB 2, 4, 2, 5, 2, 2, 4, 4
    the result will be 
    rez DW 0402h, 0304h, 0105h.
  24. Being given a string of doublewords, build another string of doublewords which will include only the doublewords from the given string which have an even number of bits with the value 1.
  25. A string of bytes is given. Obtain the mirror image of the binary representation of this string of bytes.

    Example:

    given the byte string 
    s DB 01011100b, 10001001b, 11100101b
    obtain the string 
    d DB 10100111b, 10010001b, 00111010b.
  26. A string of doublewords is given. Compute the string formed by the high bytes of the low words from the elements of the doubleword string and these bytes should be multiple of 10.

    Example:

    given the doublewords string: 
    s DD 12345678h, 1A2B3C4Dh, FE98DC76h
    obtain the string 
    d DB 3Ch, DCh.
  27. Being given a string of words, compute the longest substring of ordered words (in increasing order) from this string.
  28. Being given a string of bytes and a substring of this string, eliminate all occurrences of this substring from the initial string.
  29. Two strings of bytes A and B are given. Parse the shortest string of those two and build a third string C as follows:
    • up to the lenght of the shortest string C contains the largest element of the same rank from the two strings
    • then, up to the length of the longest string C will be filled with 1 and 0, alternatively.
  30. A string of words is given. Build two strings of bytes, s1 and s2, in the following way: for each word,
    • if the number of bits 1 from the high byte of the word is larger than the number of bits 1 from its low byte, then s1 will contain the high byte and s2 will contain the low byte of the word
    • if the number of bits 1 from the high byte of the word is equal to the number of bits 1 from its low byte, then s1 will contain the number of bits 1 from the low byte and s2 will contain 0
    • otherwise, s1 will contain the low byte and s2 will contain the high byte of the word.