Decoded: Rogue (1980) by Toy, Arnold, Wichman
DOS version (1983) by Mel Sibony and Jon Lane
Source file: STRINGS.C
Beginner friendly, line-by-line code walkthrough by MaiZure

STRINGS.C provides common string handling functions used throughout Rogue.

Original code:
https://britzl.github.io/roguearchive/

Original code with line numbers
http://www.maizure.org/projects/decoded-rogue/STRINGS_linenum.txt




1     BLANK
2     BLANK
3     Bring in a character array from elsewhere (Aztec C provided...not in Rogue)
4     BLANK
5     Returns true if input is a letter. Masks AzC char table first two bits
6     Returns true if input is upper case. Masks AzC char table first bit
7     Returns true if input is lower case. Masks AzC char table second bit
8     Returns true if input is a digit. Masks AzC char table third bit
9     Returns true if input is a space. Masks AzC char table fifth bit
10    Returns true if input is printable. Masks AzC char table (5 of 8 bits)
11    BLANK

CONVERT TO PRINTABLE ASCII

12    Defines toascii with one argument - an integer, technically
13    BLOCK START - toascii
14    Return the bottom 7 bits of the input
15    BLOCK END - toascii, converts input byte to a printable ASCII character
16    BLANK

TO UPPER CASE

17    Defines toupper with one argument
18    Argument 1 is a character
19    BLOCK START - toupper, converts input from lower to upper case
20    Returns upper case by subtracting the difference between upper and lower
      cases. I guess this was before we realized we can just set bit 5 to 0
      :)
21    BLOCK END - toupper
22    BLANK

TO LOWER CASE

23    Defines tolower with one argument
24    Argument 1 is an input character
25    BLOCK START - tolower, converts input from upper to lower case
26    Returns lower case by adding the difference between cases (if it is upper)
27    BLOCK END - tolower
28    BLANK

COPY STRINGS

29    Defines stccpy with three arguments
30    Arguments 1 and 2 are the destination and source strings
31    Argument 3 is the length of the string
32    BLOCK START - stccpy, copies strings
33    While there is still work to do...
34    Copy the strings
35    Null-terminate the string
36    COMMENT
37    COMMENT
38    COMMENT
39    COMMENT
40    Return a pointer to the *END* of the string...interesting...in 1984
41    BLOCK END - stccpy
42    BLANK
43    BLANK
44    COMMENT
45    COMMENT
46    COMMENT

SKIPS SPACES

47    stpblk returns a char pointer
48    Define stpblk with one argument
49    Argument 1 is a string (designed to be reentrant, could be in the middle
      )
50    BLOCK START - stpblk, skips blanks from a string
51    While there is a space in the string
52    Advance the pointer
53    Return the string pointer
54    BLOCK END - stpblk
55    BLANK

SKIP CERTAIN CHARACTERS

56    Defines stpbrk with two arguments  
57    Both arguments are pointers to a string and a char to be skipped
58    BLOCK START - stpbrk, skips characters in a string
59    While the desired character is at the pointer..
60    Skip it!
61    If the string is still valid reutnr it, otherwise null pointer
62    BLOCK END - stpbrk
63    BLANK
64    BLANK
65    COMMENT
66    COMMENT
67    COMMENT

REMOVE TRAILING WHITE SPACE

68    Defines endblk with one argument
69    Argument 1 is a string
70    BLOCK START - endblk, nullterms the input string without a break/space
71    Declare a local pointer to a character
72    BLANK
73    Find the last character based on length
74    While there are useless characters at this point
75    Replace all characters with zero
76    Return the patched up string pointer
77    BLOCK END - endblk
78    BLANK
79    COMMENT
80    COMMENT
81    COMMENT

CONVERT STRING TO LOWER CASE

82    Defines lcase with one agument
83    Argument 1 is an input string
84    BLOCK START - lcase, converts a string to lower case
85    While there is an upper case letter under the string, convert..
86    ..and advance the pointer
87    BLOCK END - lcase
88    EOF˙