Simplify struct scm_bignum

* libguile/integers.c (struct scm_bignum): Now that SCM_I_BIG_MPZ is
gone with other deprecated code, we can simplify the bignum
representation.  Adapt all users.

libguile/integers.c

@@ -1,4 +1,4 @@
-/* Copyright 1995-2016,2018-2022
+/* Copyright 1995-2016,2018-2022,2025
      Free Software Foundation, Inc.
 
    This file is part of Guile.
@@ -58,23 +58,14 @@ verify (SCM_MOST_POSITIVE_FIXNUM <= (mp_limb_t) -1);
 struct scm_bignum
 {
   scm_t_bits tag;
-  /* FIXME: In Guile 3.2, replace this union with just a "size" member.
-     Digits are always allocated inline.  */
-  union {
-    mpz_t mpz;
-    struct {
-      int zero;
-      int size;
-      mp_limb_t *limbs;
-    } z;
-  } u;
+  int size;
   mp_limb_t limbs[];
 };
 
 static int
 bignum_size (struct scm_bignum *z)
 {
-  return z->u.z.size;
+  return z->size;
 }
 
 static int
@@ -98,8 +89,7 @@ bignum_limb_count (struct scm_bignum *z)
 static mp_limb_t*
 bignum_limbs (struct scm_bignum *z)
 {
-  // FIXME: In the future we can just return z->limbs.
-  return z->u.z.limbs;
+  return z->limbs;
 }
 
 static inline unsigned long
@@ -151,17 +141,7 @@ allocate_bignum (size_t nlimbs)
   struct scm_bignum *z = scm_gc_malloc_pointerless (size, "bignum");
 
   z->tag = scm_tc16_big;
-
-  z->u.z.zero = 0;
-  z->u.z.size = nlimbs;
-  z->u.z.limbs = z->limbs;
-
-  // _mp_alloc == 0 means GMP will never try to free this memory.
-  ASSERT (z->u.mpz[0]._mp_alloc == 0);
-  // Our "size" field should alias the mpz's _mp_size field.
-  ASSERT (z->u.mpz[0]._mp_size == nlimbs);
-  // Limbs are always allocated inline.
-  ASSERT (z->u.mpz[0]._mp_d == z->limbs);
+  z->size = nlimbs;
 
   // z->limbs left uninitialized.
   return z;
@@ -170,24 +150,24 @@ allocate_bignum (size_t nlimbs)
 static struct scm_bignum *
 bignum_trim1 (struct scm_bignum *z)
 {
-  ASSERT (z->u.z.size > 0);
-  z->u.z.size -= (z->limbs[z->u.z.size - 1] == 0);
+  ASSERT (z->size > 0);
+  z->size -= (z->limbs[z->size - 1] == 0);
   return z;
 }
 
 static struct scm_bignum *
 bignum_trimn (struct scm_bignum *z)
 {
-  ASSERT (z->u.z.size > 0);
-  while (z->u.z.size > 0 && z->limbs[z->u.z.size - 1] == 0)
-    z->u.z.size--;
+  ASSERT (z->size > 0);
+  while (z->size > 0 && z->limbs[z->size - 1] == 0)
+    z->size--;
   return z;
 }
 
 static struct scm_bignum *
 negate_bignum (struct scm_bignum *z)
 {
-  z->u.z.size = -z->u.z.size;
+  z->size = -z->size;
   return z;
 }
 
@@ -2851,7 +2831,7 @@ do_add_1 (int negative, mp_limb_t *xd, size_t xn, mp_limb_t y)
   if (mpn_add_1 (rd, xd, xn, y))
     rd[xn] = 1;
   else
-    result->u.z.size--;
+    result->size--;
   // No need to normalize as magnitude is increasing and one operand
   // already a bignum.
   return scm_from_bignum (bignum_negate_if (negative, result));
@@ -2866,7 +2846,7 @@ do_add (int negative, mp_limb_t *xd, size_t xn, mp_limb_t *yd, size_t yn)
   if (mpn_add (rd, xd, xn, yd, yn))
     rd[xn] = 1;
   else
-    result->u.z.size--;
+    result->size--;
   // No need to normalize as magnitude is increasing and one operand
   // already a bignum.
   return scm_from_bignum (bignum_negate_if (negative, result));
@@ -3102,7 +3082,7 @@ scm_integer_mul_zi (struct scm_bignum *x, scm_t_inum y)
         if (hi)
           rd[xn] = hi;
         else
-          result->u.z.size--;
+          result->size--;
         scm_remember_upto_here_1 (x);
         return normalize_bignum (bignum_negate_if (negate, (result)));
       }