I would like to understand how exactly this conversion happens.
http://www8.cs.umu.se/~isak/Snippets/a2e.c
/*
** ASCII <=> EBCDIC conversion functions
*/
static unsigned char a2e[256] = {
0, 1, 2, 3, 55, 45, 46, 47, 22, 5, 37, 11, 12, 13, 14, 15,
16, 17, 18, 19, 60, 61, 50, 38, 24, 25, 63, 39, 28, 29, 30, 31,
64, 79,127,123, 91,108, 80,125, 77, 93, 92, 78,107, 96, 75, 97,
240,241,242,243,244,245,246,247,248,249,122, 94, 76,126,110,111,
124,193,194,195,196,197,198,199,200,201,209,210,211,212,213,214,
215,216,217,226,227,228,229,230,231,232,233, 74,224, 90, 95,109,
121,129,130,131,132,133,134,135,136,137,145,146,147,148,149,150,
151,152,153,162,163,164,165,166,167,168,169,192,106,208,161, 7,
32, 33, 34, 35, 36, 21, 6, 23, 40, 41, 42, 43, 44, 9, 10, 27,
48, 49, 26, 51, 52, 53, 54, 8, 56, 57, 58, 59, 4, 20, 62,225,
65, 66, 67, 68, 69, 70, 71, 72, 73, 81, 82, 83, 84, 85, 86, 87,
88, 89, 98, 99,100,101,102,103,104,105,112,113,114,115,116,117,
118,119,120,128,138,139,140,141,142,143,144,154,155,156,157,158,
159,160,170,171,172,173,174,175,176,177,178,179,180,181,182,183,
184,185,186,187,188,189,190,191,202,203,204,205,206,207,218,219,
220,221,222,223,234,235,236,237,238,239,250,251,252,253,254,255
};
static unsigned char e2a[256] = {
0, 1, 2, 3,156, 9,134,127,151,141,142, 11, 12, 13, 14, 15,
16, 17, 18, 19,157,133, 8,135, 24, 25,146,143, 28, 29, 30, 31,
128,129,130,131,132, 10, 23, 27,136,137,138,139,140, 5, 6, 7,
144,145, 22,147,148,149,150, 4,152,153,154,155, 20, 21,158, 26,
32,160,161,162,163,164,165,166,167,168, 91, 46, 60, 40, 43, 33,
38,169,170,171,172,173,174,175,176,177, 93, 36, 42, 41, 59, 94,
45, 47,178,179,180,181,182,183,184,185,124, 44, 37, 95, 62, 63,
186,187,188,189,190,191,192,193,194, 96, 58, 35, 64, 39, 61, 34,
195, 97, 98, 99,100,101,102,103,104,105,196,197,198,199,200,201,
202,106,107,108,109,110,111,112,113,114,203,204,205,206,207,208,
209,126,115,116,117,118,119,120,121,122,210,211,212,213,214,215,
216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,
123, 65, 66, 67, 68, 69, 70, 71, 72, 73,232,233,234,235,236,237,
125, 74, 75, 76, 77, 78, 79, 80, 81, 82,238,239,240,241,242,243,
92,159, 83, 84, 85, 86, 87, 88, 89, 90,244,245,246,247,248,249,
48, 49, 50, 51, 52, 53, 54, 55, 56, 57,250,251,252,253,254,255
};
char ASCIItoEBCDIC(const unsigned char c)
{
return a2e[c];
}
char EBCDICtoASCII(const unsigned char c)
{
return e2a[c];
}
In case of a sample text char sample[6] = "hello";, how exactly h would be converted from ascii to ebcdic and vice versa?
EDIT: I really have no need of converting a string. I just want to know how these tables were constructed.
I just want to know how these tables were constructed.
'0' in ASCII has code value of 48.
'0' in EBCDIC has code value of 240.
So we need tables that map 48 to 240 and 240 to 48.
Take converting '0' with an ASCII code value of 48. a2e[48] returns 240, the EBCDIC code for the character '0'.
static unsigned char a2e[256] = {
...
...
...
240,241,242,243,244,245,246,247,248,249,122, 94, 76,126,110,111,
...
Now use 240, the EBCDIC code for the character '0'. e2a[240] which returns 48, the ASCII code for the character '0'.
static unsigned char e2a[256] = {
...
13 more rows
...
48, 49, 50, 51, 52, 53, 54, 55, 56, 57,250,251,252,253,254,255
};
Do this for all the other common characters. Define mappings as able for the rest. Recall ASCII only defines 128 characters while EBCDIC defines 256.
Miscellanea
The EBCDIC layout has some relationship to some punch cards.
In both character sets, the characters 0, 1, ... 9 are sequential - a requirement for coding in C.
In both sets, upper case and lower case letters differ by 1 bit, so one can code the following (still better to use C's tolower())
int from_upper_to_lower(int code) {
return code - 'A' + 'a`;
}