189 lines
3.6 KiB
C
189 lines
3.6 KiB
C
/*
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FUNCTION
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<<a64l>>, <<l64a>>---convert between radix-64 ASCII string and long
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INDEX
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a64l
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INDEX
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l64a
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SYNOPSIS
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#include <stdlib.h>
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long a64l(const char *<[input]>);
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char *l64a(long <[input]>);
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DESCRIPTION
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Conversion is performed between long and radix-64 characters. The
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<<l64a>> routine transforms up to 32 bits of input value starting from
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least significant bits to the most significant bits. The input value
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is split up into a maximum of 5 groups of 6 bits and possibly one
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group of 2 bits (bits 31 and 30).
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Each group of 6 bits forms a value from 0--63 which is translated into
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a character as follows:
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O+
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o 0 = '.'
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o 1 = '/'
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o 2--11 = '0' to '9'
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o 12--37 = 'A' to 'Z'
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o 38--63 = 'a' to 'z'
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O-
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When the remaining bits are zero or all bits have been translated, a
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null terminator is appended to the string. An input value of 0
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results in the empty string.
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The <<a64l>> function performs the reverse translation. Each
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character is used to generate a 6-bit value for up to 30 bits and then
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a 2-bit value to complete a 32-bit result. The null terminator means
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that the remaining digits are 0. An empty input string or NULL string
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results in 0L. An invalid string results in undefined behavior. If
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the size of a long is greater than 32 bits, the result is sign-extended.
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RETURNS
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<<l64a>> returns a null-terminated string of 0 to 6 characters.
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<<a64l>> returns the 32-bit translated value from the input character string.
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PORTABILITY
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<<l64a>> and <<a64l>> are non-ANSI and are defined by the Single Unix Specification.
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Supporting OS subroutines required: None.
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*/
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#include <_ansi.h>
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#include <stdlib.h>
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#include <limits.h>
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long
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a64l (const char *input)
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{
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const char *ptr;
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char ch;
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int i, digit;
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unsigned long result = 0;
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if (input == NULL)
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return 0;
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ptr = input;
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/* it easiest to go from most significant digit to least so find end of input or up
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to 6 characters worth */
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for (i = 0; i < 6; ++i)
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{
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if (*ptr)
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++ptr;
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}
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while (ptr > input)
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{
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ch = *(--ptr);
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#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
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if (ch >= 'a')
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digit = (ch - 'a') + 38;
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else if (ch >= 'A')
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digit = (ch - 'A') + 12;
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else if (ch >= '0')
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digit = (ch - '0') + 2;
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else if (ch == '/')
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digit = 1;
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else
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digit = 0;
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#else /* !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__) */
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switch (ch)
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{
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case '/':
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digit = 1;
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break;
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case '0':
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case '1':
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case '2':
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case '3':
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case '4':
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case '5':
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case '6':
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case '7':
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case '8':
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case '9':
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digit = (ch - '0') + 2;
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break;
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case 'A':
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case 'B':
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case 'C':
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case 'D':
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case 'E':
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case 'F':
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case 'G':
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case 'H':
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case 'I':
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case 'J':
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case 'K':
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case 'L':
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case 'M':
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case 'N':
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case 'O':
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case 'P':
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case 'Q':
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case 'R':
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case 'S':
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case 'T':
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case 'U':
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case 'V':
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case 'W':
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case 'X':
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case 'Y':
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case 'Z':
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digit = (ch - 'A') + 12;
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break;
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case 'a':
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case 'b':
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case 'c':
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case 'd':
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case 'e':
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case 'f':
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case 'g':
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case 'h':
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case 'i':
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case 'j':
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case 'k':
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case 'l':
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case 'm':
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case 'n':
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case 'o':
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case 'p':
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case 'q':
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case 'r':
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case 's':
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case 't':
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case 'u':
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case 'v':
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case 'w':
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case 'x':
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case 'y':
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case 'z':
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digit = (ch - 'a') + 38;
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break;
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default:
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digit = 0;
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break;
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}
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#endif /* !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__) */
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result = (result << 6) + digit;
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}
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#if LONG_MAX > 2147483647
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/* for implementations where long is > 32 bits, the result must be sign-extended */
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if (result & 0x80000000)
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return (((long)-1 >> 32) << 32) + result;
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#endif
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return result;
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}
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