From 98251fc101c24e01dc2debd96a111f4202061508 Mon Sep 17 00:00:00 2001
From: Marcel Keller <mks.keller@gmail.com>
Date: Tue, 6 May 2025 12:40:09 +1000
Subject: [PATCH] Random fixed-point number generation in binary circuits.

---
 Compiler/GC/types.py | 10 +++++
 Compiler/types.py    | 88 ++++++++++++++++++++++----------------------
 2 files changed, 54 insertions(+), 44 deletions(-)

diff --git a/Compiler/GC/types.py b/Compiler/GC/types.py
index 1aae47fd..36c5bd91 100644
--- a/Compiler/GC/types.py
+++ b/Compiler/GC/types.py
@@ -841,6 +841,16 @@ class sbitvec(_vec, _bit, _binary):
                 return self.from_vec(x.zero_if_not(condition) for x in self.v)
             def __str__(self):
                 return 'sbitvec(%d)' % n
+            @classmethod
+            def get_random_int(cls, n_bits):
+                assert instructions_base.get_global_vector_size() == 1
+                return cls.from_vec(
+                    [sbit.get_random_bit() for i in range(n_bits)] + \
+                    [0] * (n - n_bits))
+            @staticmethod
+            def get_random_bit():
+                assert instructions_base.get_global_vector_size() == 1
+                return sbit.get_random_bit()
         sbitvecn.basic_type = sbitvecn
         sbitvecn.reg_type = 'sb'
         return sbitvecn
diff --git a/Compiler/types.py b/Compiler/types.py
index fb5130f2..97bd6c9a 100644
--- a/Compiler/types.py
+++ b/Compiler/types.py
@@ -4853,6 +4853,50 @@ class _fix(_single):
         assert self.f == other.f
         self.v.update(other.v)
 
+    @vectorized_classmethod
+    def get_random(cls, lower, upper, symmetric=True, public_randomness=False):
+        """ Uniform secret random number around centre of bounds.
+        Actual range can be smaller but never larger.
+
+        :param lower: float
+        :param upper: float
+        :param symmetric: symmetric distribution at higher cost
+        :param public_randomness: use public randomness (avoids preprocessing)
+        :param size: vector size (int, default 1)
+        """
+        if public_randomness:
+            get_random_int = regint.get_random
+            get_random_bit = lambda: regint.get_random(1)
+        else:
+            get_random_int = cls.int_type.get_random_int
+            get_random_bit = cls.int_type.get_random_bit
+        f = cls.f
+        k = cls.k
+        log_range = int(math.log(upper - lower, 2))
+        n_bits = log_range + cls.f
+        gen_range = (2 ** (n_bits) - 1) / 2 ** cls.f
+        diff = upper - lower
+        factor = diff / gen_range
+        real = lambda x: cfix.int_rep(x, f, k) * 2 ** -f
+        real_range = real(real(factor) * gen_range)
+        average = lower + 0.5 * (upper - lower)
+        lower = average - 0.5 * real_range
+        upper = average + 0.5 * real_range
+        r = cls._new(get_random_int(n_bits)) * factor + lower
+        if symmetric:
+            lowest = math.floor(lower * 2 ** cls.f) / 2 ** cls.f
+            highest = math.ceil(upper * 2 ** cls.f) / 2 ** cls.f
+            if program.verbose:
+                print('randomness range [%f,%f], '
+                      'fringes half the probability' % \
+                      (lowest, highest))
+            return get_random_bit().if_else(r, -r + 2 * average)
+        else:
+            if program.verbose:
+                print('randomness range [%f,%f], %d bits' % \
+                      (real(lower), real(lower) + real_range, n_bits))
+            return r
+
 class sfix(_fix):
     """ Secret fixed-point number represented as secret integer, by
     multiplying with ``2^f`` and then rounding. See :py:class:`sint`
@@ -4904,50 +4948,6 @@ class sfix(_fix):
     def get_raw_input_from(cls, player):
         return cls._new(cls.int_type.get_raw_input_from(player))
 
-    @vectorized_classmethod
-    def get_random(cls, lower, upper, symmetric=True, public_randomness=False):
-        """ Uniform secret random number around centre of bounds.
-        Actual range can be smaller but never larger.
-
-        :param lower: float
-        :param upper: float
-        :param symmetric: symmetric distribution at higher cost
-        :param public_randomness: use public randomness (avoids preprocessing)
-        :param size: vector size (int, default 1)
-        """
-        if public_randomness:
-            get_random_int = regint.get_random
-            get_random_bit = lambda: regint.get_random(1)
-        else:
-            get_random_int = cls.int_type.get_random_int
-            get_random_bit = cls.int_type.get_random_bit
-        f = cls.f
-        k = cls.k
-        log_range = int(math.log(upper - lower, 2))
-        n_bits = log_range + cls.f
-        gen_range = (2 ** (n_bits) - 1) / 2 ** cls.f
-        diff = upper - lower
-        factor = diff / gen_range
-        real = lambda x: cfix.int_rep(x, f, k) * 2 ** -f
-        real_range = real(real(factor) * gen_range)
-        average = lower + 0.5 * (upper - lower)
-        lower = average - 0.5 * real_range
-        upper = average + 0.5 * real_range
-        r = cls._new(get_random_int(n_bits)) * factor + lower
-        if symmetric:
-            lowest = math.floor(lower * 2 ** cls.f) / 2 ** cls.f
-            highest = math.ceil(upper * 2 ** cls.f) / 2 ** cls.f
-            if program.verbose:
-                print('randomness range [%f,%f], '
-                      'fringes half the probability' % \
-                      (lowest, highest))
-            return get_random_bit().if_else(r, -r + 2 * average)
-        else:
-            if program.verbose:
-                print('randomness range [%f,%f], %d bits' % \
-                      (real(lower), real(lower) + real_range, n_bits))
-            return r
-
     @classmethod
     def direct_matrix_mul(cls, A, B, n, m, l, reduce=True, indices=None):
         # pre-multiplication must be identity