On Sat, 26 Aug 2006, Jacob Yocom-Piatt wrote:
> while debugging some C code, i encountered an odd issue that i haven't seen
> before. the trouble is with spacing and nested array evaluation. the line(s)
> of
> code in question look like
Please provide a complete test program instead of some fragments. Also
specify platform and compilation options. It should not be a puzzle
to reconstruct your problem.
-Otto
>
> u_int8_t y0, y1, y2, y3;
>
> ...
>
> y0 = Q1[ Q0 [ Q0[y0] ^ b0(L[1]) ] ^ b0(L[0]) ];
> ^^
> where there is either 1 or 2 spaces after the first open square bracket and
> the
> Q's are fixed permutations [1] that map u_int8_t --> u_int8_t. if the above
> code
> is broken out like so
>
> y0 = Q0[y0] ^ b0(L[1]);
> y0 = Q0[y0] ^ b0(L[0]);
> y0 = Q1[y0];
>
> it outputs the 2-space result.
>
> i have verified that the input y0 is the same in both the 1-space and 2-space
> cases, but the results differ between the two cases. the 1-space output is
>
> a5 1f 5b 0
>
> and the 2-space output is
>
> b3 1f 5b a5.
>
> i suspect this is some C nuance of which i'm unaware. the 2-space output is
> the
> one that i expect is "correct". cluestick me please.
>
> [1] the Q permutations are global arrays which are listed below:
>
> u_int8_t
> Q0[] = {
> 0xA9, 0x67, 0xB3, 0xE8, 0x04, 0xFD, 0xA3, 0x76,
> 0x9A, 0x92, 0x80, 0x78, 0xE4, 0xDD, 0xD1, 0x38,
> 0x0D, 0xC6, 0x35, 0x98, 0x18, 0xF7, 0xEC, 0x6C,
> 0x43, 0x75, 0x37, 0x26, 0xFA, 0x13, 0x94, 0x48,
> 0xF2, 0xD0, 0x8B, 0x30, 0x84, 0x54, 0xDF, 0x23,
> 0x19, 0x5B, 0x3D, 0x59, 0xF3, 0xAE, 0xA2, 0x82,
> 0x63, 0x01, 0x83, 0x2E, 0xD9, 0x51, 0x9B, 0x7C,
> 0xA6, 0xEB, 0xA5, 0xBE, 0x16, 0x0C, 0xE3, 0x61,
> 0xC0, 0x8C, 0x3A, 0xF5, 0x73, 0x2C, 0x25, 0x0B,
> 0xBB, 0x4E, 0x89, 0x6B, 0x53, 0x6A, 0xB4, 0xF1,
> 0xE1, 0xE6, 0xBD, 0x45, 0xE2, 0xF4, 0xB6, 0x66,
> 0xCC, 0x95, 0x03, 0x56, 0xD4, 0x1C, 0x1E, 0xD7,
> 0xFB, 0xC3, 0x8E, 0xB5, 0xE9, 0xCF, 0xBF, 0xBA,
> 0xEA, 0x77, 0x39, 0xAF, 0x33, 0xC9, 0x62, 0x71,
> 0x81, 0x79, 0x09, 0xAD, 0x24, 0xCD, 0xF9, 0xD8,
> 0xE5, 0xC5, 0xB9, 0x4D, 0x44, 0x08, 0x86, 0xE7,
> 0xA1, 0x1D, 0xAA, 0xED, 0x06, 0x70, 0xB2, 0xD2,
> 0x41, 0x7B, 0xA0, 0x11, 0x31, 0xC2, 0x27, 0x90,
> 0x20, 0xF6, 0x60, 0xFF, 0x96, 0x5C, 0xB1, 0xAB,
> 0x9E, 0x9C, 0x52, 0x1B, 0x5F, 0x93, 0x0A, 0xEF,
> 0x91, 0x85, 0x49, 0xEE, 0x2D, 0x4F, 0x8F, 0x3B,
> 0x47, 0x87, 0x6D, 0x46, 0xD6, 0x3E, 0x69, 0x64,
> 0x2A, 0xCE, 0xCB, 0x2F, 0xFC, 0x97, 0x05, 0x7A,
> 0xAC, 0x7F, 0xD5, 0x1A, 0x4B, 0x0E, 0xA7, 0x5A,
> 0x28, 0x14, 0x3F, 0x29, 0x88, 0x3C, 0x4C, 0x02,
> 0xB8, 0xDA, 0xB0, 0x17, 0x55, 0x1F, 0x8A, 0x7D,
> 0x57, 0xC7, 0x8D, 0x74, 0xB7, 0xC4, 0x9F, 0x72,
> 0x7E, 0x15, 0x22, 0x12, 0x58, 0x07, 0x99, 0x34,
> 0x6E, 0x50, 0xDE, 0x68, 0x65, 0xBC, 0xDB, 0xF8,
> 0xC8, 0xA8, 0x2B, 0x40, 0xDC, 0xFE, 0x32, 0xA4,
> 0xCA, 0x10, 0x21, 0xF0, 0xD3, 0x5D, 0x0F, 0x00,
> 0x6F, 0x9D, 0x36, 0x42, 0x4A, 0x5E, 0xC1, 0xE0,
> };
>
> u_int8_t
> Q1[] = {
> 0x75, 0xF3, 0xC6, 0xF4, 0xDB, 0x7B, 0xFB, 0xC8,
> 0x4A, 0xD3, 0xE6, 0x6B, 0x45, 0x7D, 0xE8, 0x4B,
> 0xD6, 0x32, 0xD8, 0xFD, 0x37, 0x71, 0xF1, 0xE1,
> 0x30, 0x0F, 0xF8, 0x1B, 0x87, 0xFA, 0x06, 0x3F,
> 0x5E, 0xBA, 0xAE, 0x5B, 0x8A, 0x00, 0xBC, 0x9D,
> 0x6D, 0xC1, 0xB1, 0x0E, 0x80, 0x5D, 0xD2, 0xD5,
> 0xA0, 0x84, 0x07, 0x14, 0xB5, 0x90, 0x2C, 0xA3,
> 0xB2, 0x73, 0x4C, 0x54, 0x92, 0x74, 0x36, 0x51,
> 0x38, 0xB0, 0xBD, 0x5A, 0xFC, 0x60, 0x62, 0x96,
> 0x6C, 0x42, 0xF7, 0x10, 0x7C, 0x28, 0x27, 0x8C,
> 0x13, 0x95, 0x9C, 0xC7, 0x24, 0x46, 0x3B, 0x70,
> 0xCA, 0xE3, 0x85, 0xCB, 0x11, 0xD0, 0x93, 0xB8,
> 0xA6, 0x83, 0x20, 0xFF, 0x9F, 0x77, 0xC3, 0xCC,
> 0x03, 0x6F, 0x08, 0xBF, 0x40, 0xE7, 0x2B, 0xE2,
> 0x79, 0x0C, 0xAA, 0x82, 0x41, 0x3A, 0xEA, 0xB9,
> 0xE4, 0x9A, 0xA4, 0x97, 0x7E, 0xDA, 0x7A, 0x17,
> 0x66, 0x94, 0xA1, 0x1D, 0x3D, 0xF0, 0xDE, 0xB3,
> 0x0B, 0x72, 0xA7, 0x1C, 0xEF, 0xD1, 0x53, 0x3E,
> 0x8F, 0x33, 0x26, 0x5F, 0xEC, 0x76, 0x2A, 0x49,
> 0x81, 0x88, 0xEE, 0x21, 0xC4, 0x1A, 0xEB, 0xD9,
> 0xC5, 0x39, 0x99, 0xCD, 0xAD, 0x31, 0x8B, 0x01,
> 0x18, 0x23, 0xDD, 0x1F, 0x4E, 0x2D, 0xF9, 0x48,
> 0x4F, 0xF2, 0x65, 0x8E, 0x78, 0x5C, 0x58, 0x19,
> 0x8D, 0xE5, 0x98, 0x57, 0x67, 0x7F, 0x05, 0x64,
> 0xAF, 0x63, 0xB6, 0xFE, 0xF5, 0xB7, 0x3C, 0xA5,
> 0xCE, 0xE9, 0x68, 0x44, 0xE0, 0x4D, 0x43, 0x69,
> 0x29, 0x2E, 0xAC, 0x15, 0x59, 0xA8, 0x0A, 0x9E,
> 0x6E, 0x47, 0xDF, 0x34, 0x35, 0x6A, 0xCF, 0xDC,
> 0x22, 0xC9, 0xC0, 0x9B, 0x89, 0xD4, 0xED, 0xAB,
> 0x12, 0xA2, 0x0D, 0x52, 0xBB, 0x02, 0x2F, 0xA9,
> 0xD7, 0x61, 0x1E, 0xB4, 0x50, 0x04, 0xF6, 0xC2,
> 0x16, 0x25, 0x86, 0x56, 0x55, 0x09, 0xBE, 0x91,
> };
>
> cheers,
> jake
