From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 15 Feb 2007 16:38:15 +0000 (+0000)
Subject: mp-gcd, gf-gcd: Tweak memory management subtly.
X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/commitdiff_plain/3d6115d1994372d945d96c60673b302abab49cd8

mp-gcd, gf-gcd: Tweak memory management subtly.

Avoid mp churn by keeping a single spare integer lying around during the
main loop.
---

diff --git a/gf-gcd.c b/gf-gcd.c
index 9b5402b..03cee47 100644
--- a/gf-gcd.c
+++ b/gf-gcd.c
@@ -51,7 +51,7 @@ void gf_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
   mp *x = MP_ONE, *X = MP_ZERO;
   mp *y = MP_ZERO, *Y = MP_ONE;
   mp *u, *v;
-  mp *q = MP_NEW;
+  mp *q = MP_NEW, *t, *spare = MP_NEW;
   unsigned f = 0;
 
 #define f_swap 1u
@@ -69,7 +69,7 @@ void gf_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
    */
 
   if (MPX_UCMP(a->v, a->vl, <, b->v, b->vl)) {
-    { mp *t = a; a = b; b = t; }
+    t = a; a = b; b = t;
     f |= f_swap;
   }
 
@@ -112,20 +112,19 @@ void gf_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
   v = MP_COPY(b);
 
   while (!MP_ZEROP(v)) {
-    mp *t;
     gf_div(&q, &u, u, v);
     if (f & f_ext) {
-      t = gf_mul(MP_NEW, X, q);
+      t = gf_mul(spare, X, q);
       t = gf_add(t, t, x);
-      MP_DROP(x); x = X; X = t;
-      t = gf_mul(MP_NEW, Y, q);
+      spare = x; x = X; X = t;
+      t = gf_mul(spare, Y, q);
       t = gf_add(t, t, y);
-      MP_DROP(y); y = Y; Y = t;
+      spare = y; y = Y; Y = t;
     }
     t = u; u = v; v = t;
   }
 
-  MP_DROP(q);
+  MP_DROP(q); if (spare) MP_DROP(spare);
   if (!gcd)
     MP_DROP(u);
   else {
@@ -141,7 +140,7 @@ void gf_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
     /* --- If @a@ and @b@ got swapped, swap the coefficients back --- */
 
     if (f & f_swap) {
-      mp *t = x; x = y; y = t;
+      t = x; x = y; y = t;
       t = a; a = b; b = t;
     }
 
diff --git a/mp-gcd.c b/mp-gcd.c
index 2583c8e..40531c7 100644
--- a/mp-gcd.c
+++ b/mp-gcd.c
@@ -50,7 +50,7 @@ void mp_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
   mp *x = MP_ONE, *X = MP_ZERO;
   mp *y = MP_ZERO, *Y = MP_ONE;
   mp *u, *v;
-  mp *q = MP_NEW;
+  mp *q = MP_NEW, *t, *spare = MP_NEW;
   unsigned f = 0;
 
 #define f_swap 1u
@@ -74,13 +74,13 @@ void mp_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
    */
 
   if (MPX_UCMP(a->v, a->vl, <, b->v, b->vl)) {
-    { mp *t = a; a = b; b = t; }
+    t = a; a = b; b = t;
     f |= f_swap;
   }
 
   /* --- Check for zeroness --- */
 
-  if (MP_EQ(b, MP_ZERO)) {
+  if (MP_ZEROP(b)) {
 
     /* --- Store %$|a|$% as the GCD --- */
 
@@ -99,7 +99,7 @@ void mp_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
 
     if (f & f_ext) {
       if (f & f_swap) {
-	mp **t = xx; xx = yy; yy = t;
+	mp **tt = xx; xx = yy; yy = tt;
       }
       if (xx) {
 	if (*xx) MP_DROP(*xx);
@@ -132,20 +132,19 @@ void mp_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
   /* --- Main extended Euclidean algorithm --- */
 
   while (!MP_ZEROP(v)) {
-    mp *t;
     mp_div(&q, &u, u, v);
     if (f & f_ext) {
-      t = mp_mul(MP_NEW, X, q);
+      t = mp_mul(spare, X, q);
       t = mp_sub(t, x, t);
-      MP_DROP(x); x = X; X = t;
-      t = mp_mul(MP_NEW, Y, q);
+      spare = x; x = X; X = t;
+      t = mp_mul(spare, Y, q);
       t = mp_sub(t, y, t);
-      MP_DROP(y); y = Y; Y = t;
+      spare = y; y = Y; Y = t;
     }
     t = u; u = v; v = t;
   }
 
-  MP_DROP(q);
+  MP_DROP(q); if (spare) MP_DROP(spare);
   if (!gcd)
     MP_DROP(u);
   else {
@@ -166,7 +165,7 @@ void mp_gcd(mp **gcd, mp **xx, mp **yy, mp *a, mp *b)
     /* --- If @a@ and @b@ got swapped, swap the coefficients back --- */
 
     if (f & f_swap) {
-      mp *t = x; x = y; y = t;
+      t = x; x = y; y = t;
       t = a; a = b; b = t;
     }