[Rd] Spurious warnings in coercion from double/complex/character to raw

[Duncan Murdoch]

On 10/09/2021 11:29 a.m., Hervé Pagès wrote:
> Hi,
> 
> The first warning below is unexpected and confusing:
> 
>     > as.raw(c(3e9, 5.1))
>     [1] 00 05
>     Warning messages:
>     1: NAs introduced by coercion to integer range
>     2: out-of-range values treated as 0 in coercion to raw
> 
> The reason we get it is that coercion from numeric to raw is currently
> implemented on top of coercion from numeric to int (file
> src/main/coerce.c, lines 700-710):
> 
>       case REALSXP:
>           for (i = 0; i < n; i++) {
> //          if ((i+1) % NINTERRUPT == 0) R_CheckUserInterrupt();
>               tmp = IntegerFromReal(REAL_ELT(v, i), &warn);
>               if(tmp == NA_INTEGER || tmp < 0 || tmp > 255) {
>                   tmp = 0;
>                   warn |= WARN_RAW;
>               }
>               pa[i] = (Rbyte) tmp;
>           }
>           break;
> 
> The first warning comes from the call to IntegerFromReal().
> 
> The following code avoids the spurious warning and is also simpler and
> slightly faster:
> 
>       case REALSXP:
>           for (i = 0; i < n; i++) {
> //          if ((i+1) % NINTERRUPT == 0) R_CheckUserInterrupt();
>               double vi = REAL_ELT(v, i);
>               if(ISNAN(vi) || (tmp = (int) vi) < 0 || tmp > 255) {
>                   tmp = 0;
>                   warn |= WARN_RAW;
>               }
>               pa[i] = (Rbyte) tmp;
>           }
>           break;

Doesn't that give different results in case vi is so large that "(int) 
vi" overflows?  (I don't know what the C standard says, but some online 
references say that behaviour is implementation dependent.)

For example, if

   vi = 1.0 +  INT_MAX;

wouldn't "(int) vi" be equal to a small integer?

Duncan Murdoch


> 
> Coercion from complex to raw has the same problem:
> 
>     > as.raw(c(3e9+0i, 5.1))
>     [1] 00 05
>     Warning messages:
>     1: NAs introduced by coercion to integer range
>     2: out-of-range values treated as 0 in coercion to raw
> 
> Current implementation (file src/main/coerce.c, lines 711-721):
> 
>       case CPLXSXP:
>           for (i = 0; i < n; i++) {
> //          if ((i+1) % NINTERRUPT == 0) R_CheckUserInterrupt();
>               tmp = IntegerFromComplex(COMPLEX_ELT(v, i), &warn);
>               if(tmp == NA_INTEGER || tmp < 0 || tmp > 255) {
>                   tmp = 0;
>                   warn |= WARN_RAW;
>               }
>               pa[i] = (Rbyte) tmp;
>           }
>           break;
> 
> This implementation has the following additional problem when the
> supplied complex has a nonzero imaginary part:
> 
>     > as.raw(300+4i)
>     [1] 00
>     Warning messages:
>     1: imaginary parts discarded in coercion
>     2: out-of-range values treated as 0 in coercion to raw
> 
>     > as.raw(3e9+4i)
>     [1] 00
>     Warning messages:
>     1: NAs introduced by coercion to integer range
>     2: out-of-range values treated as 0 in coercion to raw
> 
> In one case we get a warning about the discarding of the imaginary part
> but not the other case, which is unexpected. We should see the exact
> same warning (or warnings) in both cases.
> 
> With the following fix we only get the warning about the discarding of
> the imaginary part if we are not in a "out-of-range values treated as 0
> in coercion to raw" situation:
> 
>       case CPLXSXP:
>           for (i = 0; i < n; i++) {
> //          if ((i+1) % NINTERRUPT == 0) R_CheckUserInterrupt();
>               Rcomplex vi = COMPLEX_ELT(v, i);
>               if(ISNAN(vi.r) || ISNAN(vi.i) || (tmp = (int) vi.r) < 0 ||
> tmp > 255) {
>                   tmp = 0;
>                   warn |= WARN_RAW;
>               } else {
>                   if(vi.i != 0.0)
>                       warn |= WARN_IMAG;
>               }
>               pa[i] = (Rbyte) tmp;
>           }
>           break;
> 
> Finally, coercion from character to raw has the same problem and its
> code can be fixed in a similar manner:
> 
>     > as.raw(c("3e9", 5.1))
>     [1] 00 05
>     Warning messages:
>     1: NAs introduced by coercion to integer range
>     2: out-of-range values treated as 0 in coercion to raw
> 
> Cheers,
> H.
> 
>