Hi all, I have noticed incorrect parsing of very small hexadecimal numbers like "0x1.00000000d0000p-987". Such a hexadecimal representation can can be produced by sprintf() using the %a flag. The return value is incorrectly reported as 0 when coercing these numbers to double using as.double()/as.numeric(), as illustrated in the three examples below:
as.double("0x1.00000000d0000p-987") # should be 7.645296e-298 as.double("0x1.0000000000000p-1022") # should be 2.225074e-308 as.double("0x1.f89fc1a6f6613p-974") # should be 1.23456e-293 The culprit seems to be the src/main/util.c:R_strtod function and in some cases, removing the zeroes directly before the 'p' leads to correct parsing: as.double("0x1.00000000dp-987") # 7.645296e-298, as expected as.double("0x1.p-1022") # 2.225074e-308, as expected I wrote a small program (in a file called "strtod.c") to compare the R stdtod implementation to a C implementation. The C implementation never reported 0 in the examples given above: #include <stdlib.h> #include <stdio.h> int main(void) { char *string, *stopstring; double x; string = "0x1.00000000d0000p-987"; x = strtod(string, &stopstring); printf("string = \"%s\"\n", string); printf("strtod = %.17g\n\n", x); string = "0x1.00000000dp-987"; x = strtod(string, &stopstring); printf("string = \"%s\"\n", string); printf("strtod = %.17g\n\n", x); } $ gcc -o strtod.exe strtod.c $ ./strtod.exe string = "0x1.00000000d0000p-987" strtod = 7.6452955642246671e-298 string = "0x1.00000000dp-987" strtod = 7.6452955642246671e-298 string = "0x1.0000000000000p-1022" strtod = 2.2250738585072014e-308 string = "0x1.p-1022" strtod = 2.2250738585072014e-308 string = "0x1.f89fc1a6f6613p-974" strtod = 1.23456e-293 My sessionInfo() returns: R version 3.3.2 (2016-10-31) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows 7 x64 (build 7601) Service Pack 1 locale: [1] LC_COLLATE=German_Switzerland.1252 LC_CTYPE=German_Switzerland.1252 LC_MONETARY=German_Switzerland.1252 LC_NUMERIC=C LC_TIME=German_Switzerland.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base Regards, Florent ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel