From f4fe05b8a2a1f288cd96be018d6dcca915e1ffe0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Albin=20Ahlb=C3=A4ck?= <albin.ahlback@gmail.com>
Date: Tue, 18 May 2021 22:52:35 +0200
Subject: [PATCH] Fix urandom stuff

---
 arb.h                |  2 +-
 arb/test/t-urandom.c |  8 ++++----
 arb/urandom.c        | 24 ++++++++++++++++++++----
 arf/urandom.c        |  4 +++-
 doc/source/arb.rst   |  4 ++--
 5 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/arb.h b/arb.h
index 35e67721..47969373 100644
--- a/arb.h
+++ b/arb.h
@@ -333,7 +333,7 @@ void arb_randtest(arb_t x, flint_rand_t state, slong prec, slong mag_bits);
 
 void arb_randtest_special(arb_t x, flint_rand_t state, slong prec, slong mag_bits);
 
-void arb_urandom(arb_t x, flint_rand_t state, slong prec, arf_rnd_t rnd);
+void arb_urandom(arb_t x, flint_rand_t state, slong prec);
 
 void arb_add_error_arf(arb_t x, const arf_t err);
 
diff --git a/arb/test/t-urandom.c b/arb/test/t-urandom.c
index 2e3dc071..41447f7b 100644
--- a/arb/test/t-urandom.c
+++ b/arb/test/t-urandom.c
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2021 Fredrik Johansson
+    Copyright (C) 2021 Albin Ahlbäck
 
     This file is part of Arb.
 
@@ -18,7 +18,6 @@ int main()
   slong iter;
   slong prec;
   flint_rand_t state;
-  arf_rnd_t round;
   arb_t rand[N];
   arb_t m; /* mean */
   arb_t s; /* variance */
@@ -34,12 +33,11 @@ int main()
   arb_init(mp);
   arb_init(sp);
   prec = 299;
-  round = ARF_RND_DOWN;
 
   for (iter = 0; iter < N; iter++)
   {
     arb_init(rand[iter]);
-    arb_urandom(rand[iter], state, prec, round);
+    arb_urandom(rand[iter], state, prec);
     arb_add(m, m, rand[iter], prec);
   }
 
@@ -77,6 +75,8 @@ int main()
   for (iter = 0; iter < N; iter++) arb_clear(rand[iter]);
   arb_clear(m);
   arb_clear(s);
+  arb_clear(mp);
+  arb_clear(sp);
   flint_randclear(state);
   flint_cleanup();
   flint_printf("PASS\n");
diff --git a/arb/urandom.c b/arb/urandom.c
index cb003208..a08e8f3c 100644
--- a/arb/urandom.c
+++ b/arb/urandom.c
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2021 Fredrik Johansson
+    Copyright (C) 2021 Albin Ahlbäck
 
     This file is part of Arb.
 
@@ -12,9 +12,25 @@
 #include "arb.h"
 
 void
-arb_urandom(arb_t x, flint_rand_t state, slong prec, arf_rnd_t rnd)
+arb_urandom(arb_t x, flint_rand_t state, slong bits)
 {
-    arf_urandom(arb_midref(x), state, prec, rnd);
-    mag_zero(arb_radref(x));
+    slong prec = bits;
+    fmpz_t n;
+    fmpz_t t;
+
+    prec += 128;
+
+    fmpz_init(n);
+    fmpz_one(n);
+    fmpz_mul_2exp(n, n, (ulong) prec);
+
+    fmpz_init(t);
+    fmpz_randm(t, state, n);
+
+    arb_set_round_fmpz(x, t, bits);
+    arb_mul_2exp_si(x, x, -prec);
+
+    fmpz_clear(n);
+    fmpz_clear(t);
 }
 
diff --git a/arf/urandom.c b/arf/urandom.c
index fa348670..dc30cd29 100644
--- a/arf/urandom.c
+++ b/arf/urandom.c
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2021 Fredrik Johansson
+    Copyright (C) 2021 Albin Ahlbäck
 
     This file is part of Arb.
 
@@ -30,5 +30,7 @@ arf_urandom(arf_t x, flint_rand_t state, slong bits, arf_rnd_t rnd)
     arf_set_round_fmpz(x, t, bits, rnd);
     arf_mul_2exp_si(x, x, -prec);
 
+    fmpz_clear(n);
     fmpz_clear(t);
 }
+
diff --git a/doc/source/arb.rst b/doc/source/arb.rst
index 8d50c963..dc1fcc52 100644
--- a/doc/source/arb.rst
+++ b/doc/source/arb.rst
@@ -373,8 +373,8 @@ Random number generation
 .. function:: void arb_urandom(arb_t x, flint_rand_t state, slong prec, arf_rnd_t rnd)
 
     Sets *x* to a uniformly distributed random number in the interval
-    `[0, 1]`. The method uses rounding from integers to floats based on the
-    rounding mode *rnd*.
+    `[0, 1]`. The method uses rounding from integers to floats, hence the
+    radius might not be `0`.
 
 Radius and interval operations
 -------------------------------------------------------------------------------