- use in-place bignum operations where available

- runs approx. 30% faster

R=r
DELTA=24  (10 added, 2 deleted, 12 changed)
OCL=32984
CL=33005

test/bench/pidigits.go

@@ -44,8 +44,6 @@ import (
 )
 
 var n = flag.Int("n", 27, "number of digits");
-
-// TODO for easier profiling, remove eventually
 var silent = flag.Bool("s", false, "don't print result");
 
 var (
@@ -61,13 +59,16 @@ func extract_digit() int64 {
 		return -1;
 	}
 
-	/* Compute (numer * 3 + accum) / denom */
-	tmp1, tmp2 = numer.MulNat(bignum.Nat(3)).Add(accum).QuoRem(denom);
+	// Compute (numer * 3 + accum) / denom
+	tmp1 = numer.Shl(1);
+	bignum.Iadd(tmp1, tmp1, numer);
+	bignum.Iadd(tmp1, tmp1, accum);
+	tmp1, tmp2 := tmp1.QuoRem(denom);
 
-	/* Now, if (numer * 4 + accum) % denom... */
-	tmp2 = tmp2.Add(numer);
+	// Now, if (numer * 4 + accum) % denom...
+	bignum.Iadd(tmp2, tmp2, numer);
 
-	/* ... is normalized, then the two divisions have the same result.  */
+	// ... is normalized, then the two divisions have the same result.
 	if tmp2.Cmp(denom) >= 0 {
 		return -1;
 	}
@@ -79,16 +80,16 @@ func next_term(k int64) {
 	y2 := k*2 + 1;
 
 	tmp1 = numer.Shl(1);
-	accum = accum.Add(tmp1);
-	accum = accum.Mul1(y2);
-	numer = numer.Mul1(k);
-	denom = denom.Mul1(y2);
+	bignum.Iadd(accum, accum, tmp1);
+	bignum.Iscale(accum, y2);
+	bignum.Iscale(numer, k);
+	bignum.Iscale(denom, y2);
 }
 
 func eliminate_digit(d int64) {
-	accum = accum.Sub(denom.Mul1(d));
-	accum = accum.Mul1(10);
-	numer = numer.Mul1(10);
+	bignum.Isub(accum, accum, denom.Mul1(d));
+	bignum.Iscale(accum, 10);
+	bignum.Iscale(numer, 10);
 }
 
 func printf(s string, arg ...) {

test/bench/timing.log

@@ -231,3 +231,10 @@ chameneos 6000000
 	gcc -O2 chameneosredux.c -lpthread	17.93u 323.65s 88.47r
 	gc chameneosredux	21.72u 0.00s 21.73r
 
+August 10 2009
+
+# In-place versions for some bignum operations.
+pidigits 10000
+	gcc -O2 pidigits.c -lgmp	2.56u 0.00s 2.57r
+	gc pidigits	55.22u 0.04s 55.29r	# *** -23%
+	gc_B pidigits	55.49u 0.02s 55.60r	# *** -23%