Primitive C pour l'elevation au carre

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@5900 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

6 files changed, 81 insertions, 1 deletions

diff --git a/otherlibs/num/bng.c b/otherlibs/num/bng.c
index 6033b6f8b1..c96af2cf28 100644
--- a/otherlibs/num/bng.c
+++ b/otherlibs/num/bng.c
@@ -271,6 +271,44 @@ static bngcarry bng_generic_mult_add
   return carry;
 }
 
+/* {a,alen} := 2 * {a,alen} + {b,blen}^2.  Return carry out.
+   Require alen >= 2 * blen. */
+static bngcarry bng_generic_square_add
+     (bng a/*[alen]*/, bngsize alen,
+      bng b/*[blen]*/, bngsize blen)
+{
+  bngcarry carry1, carry2;
+  bngsize i, aofs;
+  bngdigit ph, pl, d;
+
+  /* Double products */
+  for (carry1 = 0, i = 1; i < blen; i++) {
+    aofs = 2 * i - 1;
+    carry1 += bng_mult_add_digit(a + aofs, alen - aofs, 
+                                 b + i, blen - i, b[i - 1]);
+  }
+  /* Multiply by two */
+  carry1 = (carry1 << 1) | bng_shift_left(a, alen, 1);
+  /* Add square of digits */
+  carry2 = 0;
+  for (i = 0; i < blen; i++) {
+    d = b[i];
+    BngMult(ph, pl, d, d);
+    BngAdd2Carry(*a, carry2, *a, pl, carry2);
+    a++;
+    BngAdd2Carry(*a, carry2, *a, ph, carry2);
+    a++;
+  }
+  alen -= 2 * blen;
+  if (alen > 0 && carry2 != 0) {
+    do {
+      if (++(*a) != 0) { carry2 = 0; break; }
+      a++;
+    } while (--alen);
+  }
+  return carry1 + carry2;
+}
+
 /* {a,len-1} := {b,len} / d.  Return {b,len} modulo d.
    Require MSD of b < d.
    If BngDivNeedsNormalization is defined, require d normalized. */
@@ -378,6 +416,7 @@ struct bng_operations bng_ops = {
   bng_generic_mult_add_digit,
   bng_generic_mult_sub_digit,
   bng_generic_mult_add,
+  bng_generic_square_add,
   bng_generic_div_rem_norm_digit,
 #ifdef BngDivNeedsNormalization
   bng_generic_div_rem_digit,
diff --git a/otherlibs/num/bng.h b/otherlibs/num/bng.h
index f887e8c9fe..28c6b2d105 100644
--- a/otherlibs/num/bng.h
+++ b/otherlibs/num/bng.h
@@ -95,6 +95,13 @@ struct bng_operations {
         bng c/*[clen]*/, bngsize clen);
 #define bng_mult_add bng_ops.mult_add
 
+  /* {a,alen} := 2 * {a,alen} + {b,blen}^2.  Return carry out.
+     Require alen >= 2 * blen. */
+  bngcarry (*square_add)
+       (bng a/*[alen]*/, bngsize alen,
+        bng b/*[blen]*/, bngsize blen);
+#define bng_square_add bng_ops.square_add
+
   /* {a,len-1} := {b,len} / d.  Return {b,len} modulo d.
      Require d is normalized and MSD of b < d.
      See div_rem_digit for a function that does not require d
diff --git a/otherlibs/num/nat.ml b/otherlibs/num/nat.ml
index 02f1b1b7ad..c8c0c2fc7c 100644
--- a/otherlibs/num/nat.ml
+++ b/otherlibs/num/nat.ml
@@ -35,6 +35,7 @@ external decr_nat: nat -> int -> int -> int -> int = "decr_nat"
 external sub_nat: nat -> int -> int -> nat -> int -> int -> int -> int = "sub_nat" "sub_nat_native"
 external mult_digit_nat: nat -> int -> int -> nat -> int -> int -> nat -> int -> int = "mult_digit_nat" "mult_digit_nat_native"
 external mult_nat: nat -> int -> int -> nat -> int -> int -> nat -> int -> int -> int = "mult_nat" "mult_nat_native"
+external square_nat: nat -> int -> int -> nat -> int -> int -> int = "square_nat" "square_nat_native"
 external shift_left_nat: nat -> int -> int -> nat -> int -> int -> unit = "shift_left_nat" "shift_left_nat_native"
 external div_digit_nat: nat -> int -> nat -> int -> nat -> int -> int -> nat -> int -> unit = "div_digit_nat" "div_digit_nat_native"
 external div_nat: nat -> int -> int -> nat -> int -> int -> unit = "div_nat" "div_nat_native"
@@ -101,6 +102,10 @@ and gt_nat nat1 off1 len1 nat2 off2 len2 =
   compare_nat nat1 off1 (num_digits_nat nat1 off1 len1)
               nat2 off2 (num_digits_nat nat2 off2 len2) > 0
 
+(* XL: now implemented in C for better performance.
+   The code below doesn't handle carries correctly.
+   Fortunately, the carry is never used. *)
+(***
 let square_nat nat1 off1 len1 nat2 off2 len2 =
   let c = ref 0 
   and trash = make_nat 1 in
@@ -130,6 +135,7 @@ let square_nat nat1 off1 len1 nat2 off2 len2 =
                          (off2 + i)
     done;
   !c
+***)
 
 let gcd_int_nat i nat off len = 
   if i = 0 then 1 else
diff --git a/otherlibs/num/nat.mli b/otherlibs/num/nat.mli
index 4fadf39fc8..18cd812011 100644
--- a/otherlibs/num/nat.mli
+++ b/otherlibs/num/nat.mli
@@ -45,6 +45,7 @@ external decr_nat: nat -> int -> int -> int -> int = "decr_nat"
 external sub_nat: nat -> int -> int -> nat -> int -> int -> int -> int = "sub_nat" "sub_nat_native"
 external mult_digit_nat: nat -> int -> int -> nat -> int -> int -> nat -> int -> int = "mult_digit_nat" "mult_digit_nat_native"
 external mult_nat: nat -> int -> int -> nat -> int -> int -> nat -> int -> int -> int = "mult_nat" "mult_nat_native"
+external square_nat: nat -> int -> int -> nat -> int -> int -> int = "square_nat" "square_nat_native"
 external shift_left_nat: nat -> int -> int -> nat -> int -> int -> unit = "shift_left_nat" "shift_left_nat_native"
 external div_digit_nat: nat -> int -> nat -> int -> nat -> int -> int -> nat -> int -> unit = "div_digit_nat" "div_digit_nat_native"
 external div_nat: nat -> int -> int -> nat -> int -> int -> unit = "div_nat" "div_nat_native"
@@ -59,7 +60,6 @@ val gt_nat : nat -> int -> int -> nat -> int -> int -> bool
 external land_digit_nat: nat -> int -> nat -> int -> unit = "land_digit_nat"
 external lor_digit_nat: nat -> int -> nat -> int -> unit = "lor_digit_nat"
 external lxor_digit_nat: nat -> int -> nat -> int -> unit = "lxor_digit_nat"
-val square_nat : nat -> int -> int -> nat -> int -> int -> int
 val gcd_nat : nat -> int -> int -> nat -> int -> int -> int
 val sqrt_nat : nat -> int -> int -> nat
 val string_of_nat : nat -> string
diff --git a/otherlibs/num/nat_stubs.c b/otherlibs/num/nat_stubs.c
index bf3fa31326..a7fb7dcfe0 100644
--- a/otherlibs/num/nat_stubs.c
+++ b/otherlibs/num/nat_stubs.c
@@ -195,6 +195,20 @@ CAMLprim value mult_nat(value *argv, int argn)
                          argv[4], argv[5], argv[6], argv[7], argv[8]);
 }
 
+value square_nat_native(value nat1, value ofs1, value len1,
+                        value nat2, value ofs2, value len2)
+{
+  return
+    Val_long(bng_square_add(&Digit_val(nat1, Long_val(ofs1)), Long_val(len1),
+                            &Digit_val(nat2, Long_val(ofs2)), Long_val(len2)));
+}
+
+CAMLprim value square_nat(value *argv, int argn)
+{
+  return square_nat_native(argv[0], argv[1], argv[2],
+                           argv[3], argv[4], argv[5]);
+}
+
 value shift_left_nat_native(value nat1, value ofs1, value len1,
                             value nat2, value ofs2, value nbits)
 {
diff --git a/otherlibs/num/test/test_bng.c b/otherlibs/num/test/test_bng.c
index 4d92e43eaa..4fedcdfd56 100644
--- a/otherlibs/num/test/test_bng.c
+++ b/otherlibs/num/test/test_bng.c
@@ -344,6 +344,20 @@ int test_bng_ops(int i)
            bng2string(g, 2*p), co);
     return 1;
   }
+  /* square_add */
+  randbng(f, 2*p);
+  bng_assign(g, f, 2*p);
+  co = bng_square_add(g, 2*p, b, q);
+  BnnAssign(h, f, 2*p);
+  cp = BnnAdd(h, 2*p, h, 2*p);
+  cp += BnnMultiply(h, 2*p, b, q, b, q);
+  if (co != cp || !bngsame(g, h, 2*p)) {
+    printf("Round %d, bng_square_add(%s, %ld, %s, %ld) -> %s, %d\n",
+           i, bng2string(f, 2*p), 2*p,
+           bng2string(b, q), q,
+           bng2string(g, 2*p), co);
+    return 1;
+  }
   /* div_rem_digit */
   if (a[p - 1] < dg) {
     do_ = bng_div_rem_digit(c, a, p, dg);