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+// Inferno utils/8c/mul.c
+// http://code.google.com/p/inferno-os/source/browse/utils/8c/mul.c
+//
+// Copyright © 1994-1999 Lucent Technologies Inc. All rights reserved.
+// Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
+// Portions Copyright © 1997-1999 Vita Nuova Limited
+// Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
+// Portions Copyright © 2004,2006 Bruce Ellis
+// Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
+// Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
+// Portions Copyright © 2009 The Go Authors. All rights reserved.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+#include "gc.h"
+
+typedef struct Malg Malg;
+typedef struct Mparam Mparam;
+
+struct Malg
+{
+ char vals[10];
+};
+
+struct Mparam
+{
+ ulong value;
+ char alg;
+ char neg;
+ char shift;
+ char arg;
+ char off;
+};
+
+static Mparam multab[32];
+static int mulptr;
+
+static Malg malgs[] =
+{
+ {0, 100},
+ {-1, 1, 100},
+ {-9, -5, -3, 3, 5, 9, 100},
+ {6, 10, 12, 18, 20, 24, 36, 40, 72, 100},
+ {-8, -4, -2, 2, 4, 8, 100},
+};
+
+/*
+ * return position of lowest 1
+ */
+int
+lowbit(ulong v)
+{
+ int s, i;
+ ulong m;
+
+ s = 0;
+ m = 0xFFFFFFFFUL;
+ for(i = 16; i > 0; i >>= 1) {
+ m >>= i;
+ if((v & m) == 0) {
+ v >>= i;
+ s += i;
+ }
+ }
+ return s;
+}
+
+void
+genmuladd(Node *d, Node *s, int m, Node *a)
+{
+ Node nod;
+
+ nod.op = OINDEX;
+ nod.left = a;
+ nod.right = s;
+ nod.scale = m;
+ nod.type = types[TIND];
+ nod.xoffset = 0;
+ xcom(&nod);
+ gopcode(OADDR, d->type, &nod, d);
+}
+
+void
+mulparam(ulong m, Mparam *mp)
+{
+ int c, i, j, n, o, q, s;
+ int bc, bi, bn, bo, bq, bs, bt;
+ char *p;
+ long u;
+ ulong t;
+
+ bc = bq = 10;
+ bi = bn = bo = bs = bt = 0;
+ for(i = 0; i < nelem(malgs); i++) {
+ for(p = malgs[i].vals, j = 0; (o = p[j]) < 100; j++)
+ for(s = 0; s < 2; s++) {
+ c = 10;
+ q = 10;
+ u = m - o;
+ if(u == 0)
+ continue;
+ if(s) {
+ o = -o;
+ if(o > 0)
+ continue;
+ u = -u;
+ }
+ n = lowbit(u);
+ t = (ulong)u >> n;
+ switch(i) {
+ case 0:
+ if(t == 1) {
+ c = s + 1;
+ q = 0;
+ break;
+ }
+ switch(t) {
+ case 3:
+ case 5:
+ case 9:
+ c = s + 1;
+ if(n)
+ c++;
+ q = 0;
+ break;
+ }
+ if(s)
+ break;
+ switch(t) {
+ case 15:
+ case 25:
+ case 27:
+ case 45:
+ case 81:
+ c = 2;
+ if(n)
+ c++;
+ q = 1;
+ break;
+ }
+ break;
+ case 1:
+ if(t == 1) {
+ c = 3;
+ q = 3;
+ break;
+ }
+ switch(t) {
+ case 3:
+ case 5:
+ case 9:
+ c = 3;
+ q = 2;
+ break;
+ }
+ break;
+ case 2:
+ if(t == 1) {
+ c = 3;
+ q = 2;
+ break;
+ }
+ break;
+ case 3:
+ if(s)
+ break;
+ if(t == 1) {
+ c = 3;
+ q = 1;
+ break;
+ }
+ break;
+ case 4:
+ if(t == 1) {
+ c = 3;
+ q = 0;
+ break;
+ }
+ break;
+ }
+ if(c < bc || (c == bc && q > bq)) {
+ bc = c;
+ bi = i;
+ bn = n;
+ bo = o;
+ bq = q;
+ bs = s;
+ bt = t;
+ }
+ }
+ }
+ mp->value = m;
+ if(bc <= 3) {
+ mp->alg = bi;
+ mp->shift = bn;
+ mp->off = bo;
+ mp->neg = bs;
+ mp->arg = bt;
+ }
+ else
+ mp->alg = -1;
+}
+
+int
+m0(int a)
+{
+ switch(a) {
+ case -2:
+ case 2:
+ return 2;
+ case -3:
+ case 3:
+ return 2;
+ case -4:
+ case 4:
+ return 4;
+ case -5:
+ case 5:
+ return 4;
+ case 6:
+ return 2;
+ case -8:
+ case 8:
+ return 8;
+ case -9:
+ case 9:
+ return 8;
+ case 10:
+ return 4;
+ case 12:
+ return 2;
+ case 15:
+ return 2;
+ case 18:
+ return 8;
+ case 20:
+ return 4;
+ case 24:
+ return 2;
+ case 25:
+ return 4;
+ case 27:
+ return 2;
+ case 36:
+ return 8;
+ case 40:
+ return 4;
+ case 45:
+ return 4;
+ case 72:
+ return 8;
+ case 81:
+ return 8;
+ }
+ diag(Z, "bad m0");
+ return 0;
+}
+
+int
+m1(int a)
+{
+ switch(a) {
+ case 15:
+ return 4;
+ case 25:
+ return 4;
+ case 27:
+ return 8;
+ case 45:
+ return 8;
+ case 81:
+ return 8;
+ }
+ diag(Z, "bad m1");
+ return 0;
+}
+
+int
+m2(int a)
+{
+ switch(a) {
+ case 6:
+ return 2;
+ case 10:
+ return 2;
+ case 12:
+ return 4;
+ case 18:
+ return 2;
+ case 20:
+ return 4;
+ case 24:
+ return 8;
+ case 36:
+ return 4;
+ case 40:
+ return 8;
+ case 72:
+ return 8;
+ }
+ diag(Z, "bad m2");
+ return 0;
+}
+
+void
+shiftit(Type *t, Node *s, Node *d)
+{
+ long c;
+
+ c = (long)s->vconst & 31;
+ switch(c) {
+ case 0:
+ break;
+ case 1:
+ gopcode(OADD, t, d, d);
+ break;
+ default:
+ gopcode(OASHL, t, s, d);
+ }
+}
+
+static int
+mulgen1(ulong v, Node *n)
+{
+ int i, o;
+ Mparam *p;
+ Node nod, nods;
+
+ for(i = 0; i < nelem(multab); i++) {
+ p = &multab[i];
+ if(p->value == v)
+ goto found;
+ }
+
+ p = &multab[mulptr];
+ if(++mulptr == nelem(multab))
+ mulptr = 0;
+
+ mulparam(v, p);
+
+found:
+// print("v=%.lx a=%d n=%d s=%d g=%d o=%d \n", p->value, p->alg, p->neg, p->shift, p->arg, p->off);
+ if(p->alg < 0)
+ return 0;
+
+ nods = *nodconst(p->shift);
+
+ o = OADD;
+ if(p->alg > 0) {
+ regalloc(&nod, n, Z);
+ if(p->off < 0)
+ o = OSUB;
+ }
+
+ switch(p->alg) {
+ case 0:
+ switch(p->arg) {
+ case 1:
+ shiftit(n->type, &nods, n);
+ break;
+ case 15:
+ case 25:
+ case 27:
+ case 45:
+ case 81:
+ genmuladd(n, n, m1(p->arg), n);
+ /* fall thru */
+ case 3:
+ case 5:
+ case 9:
+ genmuladd(n, n, m0(p->arg), n);
+ shiftit(n->type, &nods, n);
+ break;
+ default:
+ goto bad;
+ }
+ if(p->neg == 1)
+ gins(ANEGL, Z, n);
+ break;
+ case 1:
+ switch(p->arg) {
+ case 1:
+ gmove(n, &nod);
+ shiftit(n->type, &nods, &nod);
+ break;
+ case 3:
+ case 5:
+ case 9:
+ genmuladd(&nod, n, m0(p->arg), n);
+ shiftit(n->type, &nods, &nod);
+ break;
+ default:
+ goto bad;
+ }
+ if(p->neg)
+ gopcode(o, n->type, &nod, n);
+ else {
+ gopcode(o, n->type, n, &nod);
+ gmove(&nod, n);
+ }
+ break;
+ case 2:
+ genmuladd(&nod, n, m0(p->off), n);
+ shiftit(n->type, &nods, n);
+ goto comop;
+ case 3:
+ genmuladd(&nod, n, m0(p->off), n);
+ shiftit(n->type, &nods, n);
+ genmuladd(n, &nod, m2(p->off), n);
+ break;
+ case 4:
+ genmuladd(&nod, n, m0(p->off), nodconst(0));
+ shiftit(n->type, &nods, n);
+ goto comop;
+ default:
+ diag(Z, "bad mul alg");
+ break;
+ comop:
+ if(p->neg) {
+ gopcode(o, n->type, n, &nod);
+ gmove(&nod, n);
+ }
+ else
+ gopcode(o, n->type, &nod, n);
+ }
+
+ if(p->alg > 0)
+ regfree(&nod);
+
+ return 1;
+
+bad:
+ diag(Z, "mulgen botch");
+ return 1;
+}
+
+void
+mulgen(Type *t, Node *r, Node *n)
+{
+ if(!mulgen1(r->vconst, n))
+ gopcode(OMUL, t, r, n);
+}
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