1 files changed, 64 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/dbl2long.c b/reference/C/CONTRIB/SNIP/dbl2long.c
new file mode 100755
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+++ b/reference/C/CONTRIB/SNIP/dbl2long.c
@@ -0,0 +1,64 @@
+/*
+**  DBL2LONG.C - Functions to round doubles to longs
+**  Public domain by Ross G. Cottrell, June 1992
+*/
+
+#include <float.h>
+#include <limits.h>
+#include <assert.h>
+
+/* Assume IEEE doubles, little-endian CPU, 32-bit 2's complement longs. */
+/* (Actually, the assumptions made here aren't quite that gross.)       */
+
+unsigned long dbl2ulong(double t)
+{
+      assert(1 == FLT_ROUNDS);
+      t += 1.0 / DBL_EPSILON;
+      return *(unsigned long *)&t;
+}
+
+long dbl2long(double t)
+{
+      assert(1 == FLT_ROUNDS);
+      t += 1.0 / DBL_EPSILON + 2.0 * (LONG_MAX + 1.0);
+      return *(long *)&t;
+}
+
+#ifdef TEST
+
+#include <stdlib.h>
+#include <math.h>
+
+int main(int argc, char **argv)
+{
+      while (*++argv)
+      {
+            printf("'%s', as a long: %ld, as an unsigned long: %lu\n",
+                  *argv, dbl2long(atof(*argv)), dbl2ulong(atof(*argv)));
+      }
+      return 0;
+}
+
+#endif /* TEST */
+
+/*
+
+EXPLANATION:
+
+The offset of 1.0/DBL_EPSILON forces the least significant bit of the
+mantissa to represent the integer 1.  This may not work on all formats of
+doubles, but I think it's a safe bet for IEEE compliant doubles, and any
+other floating point format with a radix of 2.  When this offset is added,
+the number should be rounded to the nearest representable value.  The
+assertion that FLT_ROUNDS has the value of 1 is an attempt to guarantee
+this.  You might check your float.h; if this isn't #defined as a constant 1
+you should investigate how to ensure that it will always round to the
+nearest.  If it is #defined as 1 you can safely rip out the assertions.  The
+addition of 2.0*(LONG_MAX+1.0) for the signed long is to prevent the the MSB
+of the mantissa being borrowed for negative inputs - if this happened, the
+exponent would change and the LSB of the mantissa would no longer be worth
+1.  This offset would be perfectly okay to use with the unsigned longs too
+but it's unnecessary for them, unless you want to get the answer correct
+modulo 2^^32 for negatives.
+
+*/