]> At 04:47 PM 12/10/2002 +0100, Xavier Leroy wrote: >If that was really the best approximation, there would be nothing to >argue. But both 0.10000000000000001 and 0.1 read back as identical >floats, so the latter should be printed instead, but sprintf (on >Linux at least) is too stupid to realize this. Gdtoa will supply you with the non-stupid answer, if you care to ask it. Again -- this I know well, I have used gdtoa to get specification-conforming double->String conversion in a Java VM/library. Here is a test program that demonstrates how to use gdtoa in "minimum unambiguous result length" mode. This assumes int is 32 bits long: #include "gdtoa.h" /* Always define to zero or one. It is zero on Pentium. */ #define LITTLE_ENDIAN 1 FPI d_convert = { 53, 1-1023-53+1, 2046-1023-53+1, FPI_Round_near, 0}; union pun { double d; int i[2]; }; char * test_gdtoa(double d, int mode, int ndigits, int * plength, int * pdecpt) { union pun convert; convert.d = d; { int i0 = convert.i[0^LITTLE_ENDIAN]; int i1 = convert.i[1^LITTLE_ENDIAN]; int isNeg = i0 < 0; int m0 = i0 & 0xfffff; int e0 = ((unsigned)i0 >> 20) & 0x7ff; int int_args[8]; char * ptr_args[1]; char * result; int length; /* NaN or Inf */ if (e0 == 0x7ff) { if ((m0 | i1) != 0) { *plength = -1; return "NaN"; } else { *plength = -1; return isNeg ? "-Infinity" : "Infinity"; } } /* +/- 0 */ if ((m0 | i1 | e0) == 0) { *plength = -1; return isNeg ? "-0.0" : "0.0"; } /* If the exponent is larger than zero, then the leading "1" in the mantisssa is implicit. Otherwise, the number is denormalized, and the exponent is really 1. */ if (e0 != 0) m0 |= 0x100000; else e0 = 1; /* Adjust exponent to remove bias and to make the mantissa all "integer", e.g. 12345e-4 instead of 1.2345e+0 */ e0 -= 0x3ff + 52; int_args[0] = i1; int_args[1] = m0; int_args[2] = STRTOG_Normal; result = gdtoa(&d_convert, /* fpi */ e0, /* be */ int_args + 0, /* bits */ int_args + 2, /* kindP */ mode, /* mode */ ndigits, /* ndigits */ int_args + 3, /* decpt */ ptr_args + 0); /* rve */ *pdecpt = int_args[3]; length = ptr_args[0] - result; if (length == 0) { *plength = -1; return isNeg ? "-0.0" : "0.0"; } *plength = length; return result; } } static test_one(double d) { int decpt; int length; char * result = test_gdtoa(d, 0, 0, &length, &decpt); if (length == -1) { printf("test of %f returns special value %s\n", d, result); } else { printf("test of %f returns regular value %s, decpt %d, length %d\n", d, result, decpt, length); } } int main(int argc, char ** argv) { test_one(1.0); test_one(1.0/0.0); test_one(-1.0/0.0); test_one(-1.0/0.0 + 1.0/0.0); test_one(0.0); test_one(-0.0); test_one(-1.0); test_one(0.25); test_one(4.0); test_one(8192.125); test_one(0.1); test_one(0.01); test_one(0.9); test_one(0.09); test_one(0.2); test_one(0.02); test_one(0.3); test_one(0.03); } David Chase ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners