[Rd] Accessing Raw Mode Vectors from .C (PR#7853)

[keithf at amnis.com]

Full_Name: Keith Frost
Version: 2.0.0
OS: Linux i686 (RH 9)
Submission from: (NULL) (66.162.141.10)



If I create the C function:

void test_raw(unsigned char *raw, int *out)
{
  int i;
  for (i = 0; i <= 255; i++)
    out[i] = raw[i];
}

and dyn.load the resulting library, then call

.C("test_raw", as.raw(255:0), integer(256), DUP=FALSE)[[2]];

the result is 
  [1]  24   0   0 224 160 116  31   8   0 158  93   8 160 184 107   8   0   1
 [19]   0   0 111  34  41   0 255 254 253 252 251 250 249 248 247 246 245 244
 [37] 243 242 241 240 239 238 237 236 235 234 233 232 231 230 229 228 227 226
 [55] 225 224 223 222 221 220 219 218 217 216 215 214 213 212 211 210 209 208
... <10 deleted lines> ...
[253]  27  26  25  24

It appears that the C code gets a pointer which points 25 bytes before the
beginning of the raw vector data in memory.  I know that this is not documented
to work, but it would be a *very* nice feature to have, and it looks like it
*almost* works....  Hence this bug report.