From 2b0d84761577dea4fc5282593305440290ab1696 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Mon, 28 Mar 2022 14:16:57 -0400
Subject: modernize big_sub()

---
 big.c | 59 ++++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 42 insertions(+), 17 deletions(-)

diff --git a/big.c b/big.c
index c35ce99..49d9598 100644
--- a/big.c
+++ b/big.c
@@ -171,8 +171,8 @@ word bigsub(word x, word y)
   return (big_sub(y, x));	/* both negative */
 }
 
-word big_sub(x, y)		/* ignore input signs, treat x,y as positive */
-word x, y;
+/* ignore input signs, treat x,y as positive */
+word big_sub(word x, word y)
 {
   word d = digit0(x) - digit0(y);
   word borrow = (d & IBASE) != 0;
@@ -181,63 +181,88 @@ word x, y;
   word *p = NULL;		/* pointer to trailing zeros, if any */
   x = rest(x);
   y = rest(y);
-  while (x && y) {		/* this loop has been unwrapped once, see above */
+
+  /* this loop has been unwrapped once, see above */
+  while (x && y) {
     d = digit(x) - digit(y) - borrow;
     borrow = (d & IBASE) != 0;
     d = d & MAXDIGIT;
     *z = make(INT, d, 0);
-    if (d)
+
+    if (d) {
       p = NULL;
-    else if (!p)
+    } else if (!p) {
       p = z;
+    }
+
     x = rest(x);
     y = rest(y);
     z = &rest(*z);
   }
-  while (y) {			/* at most one of these two loops will be invoked */
+
+  /* at most one of these two loops will be invoked */
+  while (y) {
     d = -digit(y) - borrow;
     borrow = ((d & IBASE) != 0);
     d = d & MAXDIGIT;
     *z = make(INT, d, 0);
-    if (d)
+
+    if (d) {
       p = NULL;
-    else if (!p)
+    } else if (!p) {
       p = z;
+    }
+
     y = rest(y);
     z = &rest(*z);
   }
-  while (x) {			/* alternative loop */
+
+  /* alternative loop */
+  while (x) {
     d = digit(x) - borrow;
     borrow = ((d & IBASE) != 0);
     d = d & MAXDIGIT;
     *z = make(INT, d, 0);
-    if (d)
+
+    if (d) {
       p = NULL;
-    else if (!p)
+    } else if (!p) {
       p = z;
+    }
+
     x = rest(x);
     z = &rest(*z);
   }
-  if (borrow) {			/* result is negative  - take complement and add 1 */
+
+  /* result is negative  - take complement and add 1 */
+  if (borrow) {
     p = NULL;
     d = (digit(r) ^ MAXDIGIT) + 1;
     borrow = ((d & IBASE) != 0);	/* borrow now means `carry' (sorry) */
     digit(r) = SIGNBIT | d;	/* set sign bit of result */
     z = &rest(r);
+
     while (*z) {
       d = (digit(*z) ^ MAXDIGIT) + borrow;
       borrow = ((d & IBASE) != 0);
       digit(*z) = d = d & MAXDIGIT;
-      if (d)
+
+      if (d) {
 	p = NULL;
-      else if (!p)
+      } else if (!p) {
 	p = z;
+      }
+
       z = &rest(*z);
     }
   }
-  if (p)
-    *p = 0;			/* remove redundant (ie trailing) zeros */
-  return (r);
+
+  /* remove redundant (ie trailing) zeros */
+  if (p) {
+    *p = 0;
+  }
+
+  return r;
 }
 
 int bigcmp(x, y)		/* returns +ve,0,-ve as x greater than, equal, less than y */
-- 
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