From 69a209875107dce06174442d214c92f2fe748aae Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Mon, 28 Mar 2022 16:01:27 -0400
Subject: modify longdiv() and shortdiv() to return structs, eliminating
 another global, rename bigdiv() and bigmod() to big_divide() and
 big_remainder() to ensure no call sights are missed

---
 big.c    | 61 +++++++++++++++++++++++++++++++++++--------------------------
 big.h    |  4 ++--
 reduce.c | 10 +++++-----
 3 files changed, 42 insertions(+), 33 deletions(-)

diff --git a/big.c b/big.c
index a30f890..4ea8726 100644
--- a/big.c
+++ b/big.c
@@ -24,16 +24,21 @@
 #define OCTW 5          /* number of factors of 8 in IBASE */
 #define DIGITWIDTH 15
 
+struct big_div {
+  word quo;
+  word rem;
+};
+
 word big_one;
 
 static word big_plus(word, word, int);
 static word big_sub(word, word);
 static word len(word);
-static word longdiv(word, word);
+static struct big_div big__longdiv(word, word);
+static struct big_div shortdiv(word, word);
 static word ms2d(word);
 static word msd(word);
 static word shift(word, word);
-static word shortdiv(word, word);
 static word stimes(word, word);
 
 void bigsetup(void)
@@ -359,11 +364,8 @@ word stimes(word x, word n)
   return r;
 }
 
-/* TODO: make bigdiv()/bigmod() behave like div()/ldiv()/lldiv() */
-word b_rem;			/* contains remainder from last call to longdiv or shortdiv */
-
 /* may assume y~=0 */
-word bigdiv(word x, word y)
+word big_divide(word x, word y)
 {
   word s1 = big_is_negative(y);
   word s2 = s1;
@@ -379,10 +381,11 @@ word bigdiv(word x, word y)
     s2 = !s1;
   }
 
-  word q = rest(y) ? longdiv(x, y) : shortdiv(x, digit(y));
+  struct big_div bd = rest(y) ? big__longdiv(x, y) : shortdiv(x, digit(y));
+  word q = bd.quo;
 
   if (s2) {
-    if (!bigzero(b_rem)) {
+    if (!bigzero(bd.rem)) {
       x = q;
       while ((digit(x) += 1) == IBASE) {	/* add 1 to q in situ */
 	digit(x) = 0;
@@ -402,7 +405,7 @@ word bigdiv(word x, word y)
 }
 
 /* may assume y~=0 */
-word bigmod(word x, word y)
+word big_remainder(word x, word y)
 {
   word s1 = big_is_negative(y);
   word s2 = s1;
@@ -412,24 +415,21 @@ word bigmod(word x, word y)
     y = make(INT, digit0(y), rest(y));
   }
 
+  /* effect: s1 set iff y negative, s2 set iff signs mixed */
   if (big_is_negative(x)) {
     x = make(INT, digit0(x), rest(x));
     s2 = !s1;
   }
 
-  /* effect: s1 set iff y negative, s2 set iff signs mixed */
-  if (rest(y)) {
-    longdiv(x, y);
-  } else {
-    shortdiv(x, digit(y));
-  }
+  struct big_div bd = rest(y) ? big__longdiv(x, y) : shortdiv(x, digit(y));
 
   if (s2) {
-    if (!bigzero(b_rem)) {
-      b_rem = bigsub(y, b_rem);
+    if (!bigzero(bd.rem)) {
+      bd.rem = bigsub(y, bd.rem);
     }
   }
-  return (s1 ? bignegate(b_rem) : b_rem);
+
+  return (s1 ? bignegate(bd.rem) : bd.rem);
 }
 
 /* NB - above have entier based handling of signed cases  (as  Miranda)  in
@@ -444,7 +444,7 @@ word bigmod(word x, word y)
 /* divide big x by single digit n returning big quotient
    and setting external b_rem as side effect */
 /* may assume - x>=0,n>0 */
-word shortdiv(word x, word n)
+struct big_div shortdiv(word x, word n)
 {
   word d = digit(x);
   word q = 0;
@@ -477,18 +477,24 @@ word shortdiv(word x, word n)
     q = tmp;
   }
 
-  b_rem = make(INT, s_rem, 0);
-  return q;
+  struct big_div bd = {
+    .quo = q,
+    .rem = make(INT, s_rem, 0),
+  };
+  return bd;
 }
 
 /* divide big x by big y returning quotient, leaving
    remainder in extern variable b_rem */
 /* may assume - x>=0,y>0 */
-word longdiv(word x, word y)
+struct big_div big__longdiv(word x, word y)
 {
   if (bigcmp(x, y) < 0) {
-    b_rem = x;
-    return (make(INT, 0, 0));
+    struct big_div bd = {
+      .quo = make(INT, 0, 0),
+      .rem = x,
+    };
+    return bd;
   }
 
   word y1 = msd(y);
@@ -546,8 +552,11 @@ word longdiv(word x, word y)
 
     q = make(INT, d, q);
     if (n-- == 0) {
-      b_rem = scale == 1 ? x : shortdiv(x, scale);
-      return (q);
+      struct big_div bd = {
+        .quo = q,
+        .rem = scale == 1 ? x : shortdiv(x, scale).rem,
+      };
+      return bd;
     }
     ly--;
     y = rest(y);
diff --git a/big.h b/big.h
index d291512..50099dd 100644
--- a/big.h
+++ b/big.h
@@ -28,8 +28,8 @@ double bigtodbl(word);
 double biglog(word);
 double biglog10(word);
 int bigcmp(word,word);
-word bigdiv(word,word);
-word bigmod(word,word);
+word big_divide(word, word);
+word big_remainder(word,word);
 word bignegate(word);
 word bigoscan(char *,char *);
 word bigplus(word,word);
diff --git a/reduce.c b/reduce.c
index 562d611..6f41d50 100644
--- a/reduce.c
+++ b/reduce.c
@@ -2075,8 +2075,8 @@ L3: if(arg1==NIL)lexfail(lastarg);
     GETARG(arg1);
     UPLEFT;
     if(tag[arg1]==DOUBLE||tag[lastarg]==DOUBLE)int_error("div");
-    if(bigzero(lastarg))div_error();  /* build into bigmod ? */
-    simpl(bigdiv(arg1,lastarg));
+    if(bigzero(lastarg))div_error();  /* build into big_remainder ? */
+    simpl(big_divide(arg1,lastarg));
     goto DONE;
 
     case READY(FDIV):
@@ -2086,7 +2086,7 @@ L3: if(arg1==NIL)lexfail(lastarg);
     /* experiment, suppressed
     if(tag[lastarg]==INT&&tag[arg1]==INT&&!bigzero(lastarg))
       { extern word b_rem;
-	int d = bigdiv(arg1,lastarg);
+	int d = big_divide(arg1,lastarg);
 	if(bigzero(b_rem)){ simpl(d); goto DONE; }
       } /* makes a/b integer if a, b integers dividing exactly */
     fa=force_dbl(arg1);
@@ -2100,8 +2100,8 @@ L3: if(arg1==NIL)lexfail(lastarg);
     GETARG(arg1);
     UPLEFT;
     if(tag[arg1]==DOUBLE||tag[lastarg]==DOUBLE)int_error("mod");
-    if(bigzero(lastarg))div_error();  /* build into bigmod ? */
-    simpl(bigmod(arg1,lastarg));
+    if(bigzero(lastarg))div_error();  /* build into big_remainder ? */
+    simpl(big_remainder(arg1,lastarg));
     goto DONE;
 
     case READY(POWER):
-- 
cgit v1.2.1