llvm: Implement range integer generation to match Python's

Uses bit masked rejection sampling.
Matches to Python's Random.randrange API call.

Signed-off-by: Jan Vesely <[email protected]>

psyneulink/core/llvm/builtins.py

@@ -658,10 +658,11 @@ def _setup_mt_rand_init(ctx, state_ty, init_scalar):
     return builder.function
 
 
-def _setup_mt_rand_integer(ctx, state_ty):
+def _setup_mt_rand_int32(ctx, state_ty):
     int64_ty = ir.IntType(64)
+
     # Generate random number generator function.
-    # It produces random 32bit numberin a 64bit word
+    # It produces random 32bit number in a 64bit word
     builder = _setup_builtin_func_builder(ctx, "mt_rand_int32", (state_ty.as_pointer(), int64_ty.as_pointer()))
     state, out = builder.function.args
 
@@ -759,6 +760,44 @@ def _setup_mt_rand_integer(ctx, state_ty):
 
     return builder.function
 
+
+def _setup_rand_bounded_int32(ctx, state_ty, gen_int32):
+
+    out_ty = gen_int32.args[1].type.pointee
+    builder = _setup_builtin_func_builder(ctx, gen_int32.name + "_bounded", (state_ty.as_pointer(), ctx.int32_ty, ctx.int32_ty, out_ty.as_pointer()))
+    state, lower, upper, out_ptr = builder.function.args
+
+    rand_range_excl = builder.sub(upper, lower)
+
+    range_leading_zeros_in32bit = builder.ctlz(rand_range_excl, ctx.bool_ty(1))
+    range_leading_zeros_in32bit = builder.zext(range_leading_zeros_in32bit, out_ty)
+
+    rand_range_excl = builder.zext(rand_range_excl, out_ty)
+
+    loop_block = builder.append_basic_block("bounded_loop_block")
+    out_block = builder.append_basic_block("bounded_out_block")
+
+    builder.branch(loop_block)
+
+    # Loop:
+    # do:
+    #   r = random() >> INT_BITS - num_bits # num_bits = INT_BITS - leading zeros
+    # while r >= limit
+    builder.position_at_end(loop_block)
+
+    builder.call(gen_int32, [state, out_ptr])
+    val = builder.load(out_ptr)
+    val = builder.lshr(val, range_leading_zeros_in32bit)
+
+    is_above_limit = builder.icmp_unsigned(">=", val, rand_range_excl)
+    builder.cbranch(is_above_limit, loop_block, out_block)
+
+    builder.position_at_end(out_block)
+    offset = builder.zext(lower, val.type)
+    result = builder.add(val, offset)
+    builder.store(result, out_ptr)
+    builder.ret_void()
+
 def _setup_mt_rand_float(ctx, state_ty, gen_int):
     """
     Mersenne Twister double prcision random number generation.
@@ -893,8 +932,9 @@ def setup_mersenne_twister(ctx):
     init_scalar = _setup_mt_rand_init_scalar(ctx, state_ty)
     _setup_mt_rand_init(ctx, state_ty, init_scalar)
 
-    gen_int = _setup_mt_rand_integer(ctx, state_ty)
-    gen_float = _setup_mt_rand_float(ctx, state_ty, gen_int)
+    gen_int32 = _setup_mt_rand_int32(ctx, state_ty)
+    _setup_rand_bounded_int32(ctx, state_ty, gen_int32)
+    gen_float = _setup_mt_rand_float(ctx, state_ty, gen_int32)
     _setup_mt_rand_normal(ctx, state_ty, gen_float)
     _setup_rand_binomial(ctx, state_ty, gen_float, prefix="mt")
 

tests/llvm/test_builtins_mt_random.py

@@ -6,6 +6,64 @@
 
 SEED = 0
 
+@pytest.mark.benchmark(group="Mersenne Twister bounded integer PRNG")
+@pytest.mark.parametrize('mode', ['Python',
+                                  pytest.param('LLVM', marks=pytest.mark.llvm),
+                                  pytest.helpers.cuda_param('PTX')])
+@pytest.mark.parametrize("bounds, expected",
+    [((0xffffffff,), [3626764237, 1654615998, 3255389356, 3823568514, 1806341205]),
+     ((14,), [13, 6, 12, 6, 0]),
+     ((0,14), [13, 6, 12, 6, 0]),
+     ((5,0xffff), [55345, 25252, 49678, 58348, 27567]),
+    ], ids=lambda x: str(x) if len(x) != 5 else "")
+def test_random_int32_bounded(benchmark, mode, bounds, expected):
+
+    res = []
+    if mode == 'Python':
+        state = random.Random(SEED)
+
+        def f():
+            # Python randrange is exclusive upper bound
+            return state.randrange(*bounds)
+
+    elif mode == 'LLVM':
+        init_fun = pnlvm.LLVMBinaryFunction.get('__pnl_builtin_mt_rand_init')
+        state = init_fun.np_buffer_for_arg(0)
+
+        init_fun(state, SEED)
+
+        gen_fun = pnlvm.LLVMBinaryFunction.get('__pnl_builtin_mt_rand_int32_bounded')
+
+        def f():
+            lower, upper = bounds if len(bounds) == 2 else (0, bounds[0])
+            out = gen_fun.np_buffer_for_arg(3)
+            gen_fun(state, lower, upper, out)
+            return out
+
+    elif mode == 'PTX':
+        init_fun = pnlvm.LLVMBinaryFunction.get('__pnl_builtin_mt_rand_init')
+
+        state_size = init_fun.np_buffer_for_arg(0).nbytes
+        gpu_state = pnlvm.jit_engine.pycuda.driver.mem_alloc(state_size)
+
+        init_fun.cuda_call(gpu_state, np.int32(SEED))
+
+        gen_fun = pnlvm.LLVMBinaryFunction.get('__pnl_builtin_mt_rand_int32_bounded')
+        out = gen_fun.np_buffer_for_arg(3)
+        gpu_out = pnlvm.jit_engine.pycuda.driver.Out(out)
+
+        def f():
+            lower, upper = bounds if len(bounds) == 2 else (0, bounds[0])
+            gen_fun.cuda_call(gpu_state, np.uint32(lower), np.uint32(upper), gpu_out)
+            return out.copy()
+
+    else:
+        assert False, "Unknown mode: {}".format(mode)
+
+    res = [f(), f(), f(), f(), f()]
+    np.testing.assert_allclose(res, expected)
+    benchmark(f)
+
 @pytest.mark.benchmark(group="Mersenne Twister integer PRNG")
 @pytest.mark.parametrize('mode', ['Python', 'numpy',
                                   pytest.param('LLVM', marks=pytest.mark.llvm),