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Changed sexp_double_to_bignum to extract "digits" in base-16 rather

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than base 10 so no round-off errors occur at each step.  This is
assuming FLT_RADIX is 2,4,8 or 16.
This commit is contained in:
Jim Rees 2018-03-23 10:36:37 -04:00
parent b25e46b11b
commit 17eb19e43d
1 changed files with 5 additions and 3 deletions
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8
bignum.c
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@ -67,6 +67,8 @@ sexp sexp_make_unsigned_integer (sexp ctx, sexp_luint_t x) {
#define double_trunc_10s_digit(f) (trunc((f)/10.0)*10.0)
#define double_10s_digit(f) ((f)-double_trunc_10s_digit(f))
#define double_16s_digit(f) fmod(f,16.0)
sexp sexp_double_to_bignum (sexp ctx, double f) {
int sign;
sexp_gc_var3(res, scale, tmp);
@ -74,10 +76,10 @@ sexp sexp_double_to_bignum (sexp ctx, double f) {
res = sexp_fixnum_to_bignum(ctx, SEXP_ZERO);
scale = sexp_fixnum_to_bignum(ctx, SEXP_ONE);
sign = (f < 0 ? -1 : 1);
for (f=fabs(f); f >= 1.0; f=trunc(f/10)) {
tmp = sexp_bignum_fxmul(ctx, NULL, scale, (sexp_uint_t)double_10s_digit(f), 0);
for (f=fabs(f); f >= 1.0; f=trunc(f/16)) {
tmp = sexp_bignum_fxmul(ctx, NULL, scale, (sexp_uint_t)double_16s_digit(f), 0);
res = sexp_bignum_add(ctx, res, res, tmp);
scale = sexp_bignum_fxmul(ctx, NULL, scale, 10, 0);
scale = sexp_bignum_fxmul(ctx, NULL, scale, 16, 0);
}
sexp_bignum_sign(res) = sign;
sexp_gc_release3(ctx);