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vm: some fixes to fast bignum gcd.

db4
John Benediktsson 2012-08-03 12:13:46 -07:00
parent a4a62524b3
commit 37001708cd
1 changed files with 13 additions and 19 deletions
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32
vm/bignum.cpp
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@ -1768,10 +1768,10 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
{ {
GC_BIGNUM(a); GC_BIGNUM(a);
GC_BIGNUM(b); GC_BIGNUM(b);
bignum *c, *d, *e, *f, *g; bignum *c, *d, *e;
bignum_twodigit_type x, y, q, s, t, A, B, C, D; bignum_twodigit_type x, y, q, s, t, A, B, C, D;
int nbits, k; int nbits, k;
bignum_length_type size_a, size_b; bignum_length_type size_a, size_b, size_d;
bignum_digit_type *scan_a, *scan_b, *scan_c, *scan_d, *a_end, *b_end; bignum_digit_type *scan_a, *scan_b, *scan_c, *scan_d, *a_end, *b_end;
/* clone the bignums so we can modify them in-place */ /* clone the bignums so we can modify them in-place */
@ -1797,8 +1797,11 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
/* Initial reduction: make sure that 0 <= b <= a. */ /* Initial reduction: make sure that 0 <= b <= a. */
if (bignum_compare(a, b) == bignum_comparison_less) { if (bignum_compare(a, b) == bignum_comparison_less) {
d = a; d = a;
size_d = size_a;
a = b; a = b;
size_a = size_b;
b = d; b = d;
size_b = size_d;
} }
while (size_a > 1) { while (size_a > 1) {
@ -1832,21 +1835,17 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
if (k == 0) { if (k == 0) {
/* no progress; do a Euclidean step */ /* no progress; do a Euclidean step */
if (BIGNUM_LENGTH (b) == 0) { if (size_b == 0) {
return a; return a;
} }
e = bignum_trim (a); e = bignum_remainder (a, b);
GC_BIGNUM(e); GC_BIGNUM(e);
f = bignum_trim (b); if (e == BIGNUM_OUT_OF_BAND) {
GC_BIGNUM(f); return e;
g = bignum_remainder (e, f);
GC_BIGNUM(g);
if (g == BIGNUM_OUT_OF_BAND) {
return g;
} }
a = b; a = b;
size_a = BIGNUM_LENGTH (a); size_a = size_b;
b = g; b = e;
size_b = BIGNUM_LENGTH (b); size_b = BIGNUM_LENGTH (b);
continue; continue;
} }
@ -1907,14 +1906,9 @@ bignum * factor_vm::bignum_gcd(bignum * a, bignum * b)
while (size_b > 0 && *(--scan_b) == 0) size_b--; while (size_b > 0 && *(--scan_b) == 0) size_b--;
} }
e = bignum_trim (a);
GC_BIGNUM(e);
f = bignum_trim (b);
GC_BIGNUM(f);
/* a fits into a fixnum, so b must too */ /* a fits into a fixnum, so b must too */
fixnum xx = bignum_to_fixnum (e); fixnum xx = bignum_to_fixnum (a);
fixnum yy = bignum_to_fixnum (f); fixnum yy = bignum_to_fixnum (b);
fixnum tt; fixnum tt;
/* usual Euclidean algorithm for longs */ /* usual Euclidean algorithm for longs */