From 69a80c94b979fec0ab3032cfc636b801a204b2ed Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Thu, 25 Jul 2024 14:49:45 +0900
Subject: [PATCH] mruby-bigint (mpz_and): support bit-wise `and` with negative
 numbers

Negative integers are virtually considered as 2's compliment of the
absolute value of the corresponding number. It means `-1` is considered
as infinite sequence of `1` toward msb side. ref #6314
---
 mrbgems/mruby-bigint/core/bigint.c | 84 +++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 12 deletions(-)

diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index 81dffcbc5..e22601bd7 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -867,19 +867,79 @@ mpz_neg(mrb_state *mrb, mpz_t *x, mpz_t *y)
 }
 
 static void
-mpz_and(mrb_state *mrb, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient way to do this */
+mpz_2comp(mrb_state *mrb, mpz_t *x)
 {
-  size_t sz = imin(x->sz, y->sz);
+  size_t i = x->sz;
+  uint32_t *ds = x->p;
+  uint64_t num;
 
-  mpz_realloc(mrb, z, sz);
-  for (size_t i=0; i < sz; i++)
-    z->p[i] = x->p[i] & y->p[i];
-  if (x->sn < 0 && y->sn < 0)
-    z->sn = (-1);
-  else
-    z->sn = 1;
-  if (uzero(z))
-    z->sn = 0;
+  if (!i) return;
+  while (i--) ds[i] = ~ds[i];
+  i = 0; num = 1;
+  do {
+    num += ds[i];
+    ds[i++] = LOW(num);
+    num >>= DIG_SIZE;
+  } while (i < x->sz);
+  if (num != 0) {
+    mpz_realloc(mrb, x, x->sz + 1);
+    ds = x->p;
+    ds[x->sz-1] = x->sn > 0 ? ~0 : 1;
+  }
+}
+
+void
+mpz_and(mrb_state *mrb, mpz_t *z, mpz_t *x, mpz_t *y)
+{
+  if (x->sn == 0 || y->sn == 0) {
+    zero(z);
+    return;
+  }
+  mrb_assert(x->sz > 0 || y->sz > 0);
+
+  z->sn = x->sn < 0 && y->sn < 0 ? -1 : 1;
+
+  mpz_t xx, yy;
+  if (x->sn < 0) {
+    mpz_init_set(mrb, &xx, x);
+    x = &xx;
+    mpz_2comp(mrb, x);
+  }
+  if (y->sn < 0) {
+    mpz_init_set(mrb, &yy, y);
+    y = &yy;
+    mpz_2comp(mrb, y);
+  }
+
+  uint32_t *ds1, *ds2, *zds;
+  size_t l1, l2;
+  short sign;
+
+  if (x->sz > y->sz) {
+    l1 = y->sz;
+    l2 = x->sz;
+    ds1 = y->p;
+    ds2 = x->p;
+    sign = y->sn;
+  }
+  else {
+    l1 = x->sz;
+    l2 = y->sz;
+    ds1 = x->p;
+    ds2 = y->p;
+    sign =x->sn;
+  }
+  mpz_realloc(mrb, z, l2);
+  zds = z->p;
+
+  size_t i;
+  for (i=0; i<l1; i++) {
+    zds[i] = ds1[i] & ds2[i];
+  }
+  for (; i<l2; i++) {
+    zds[i] = sign>0?0:ds2[i];
+  }
+  if (z->sn < 0) mpz_2comp(mrb, z);
 }
 
 static void
@@ -1509,7 +1569,7 @@ mrb_bint_and(mrb_state *mrb, mrb_value x, mrb_value y)
 
   if (mrb_integer_p(y)) {
     mrb_int z = mrb_integer(y);
-    if (z < DIG_BASE) {
+    if (z >= 0 && z < DIG_BASE) {
       z &= b1->mp.p[0];
       return mrb_int_value(mrb, z);
     }