Merge pull request #297 from bashtage/fix-rangomgen-advance

BUG: Correct advance on systems without int128

randomgen/common.pyx

@@ -50,9 +50,8 @@ cdef class BitGenerator:
         if isinstance(seed, ISEED_SEQUENCES):
             if mode == "legacy":
                 raise ValueError("seed is a SeedSequence instance but mode is "
-                                 "\"legacy\". Using a SeedSequence implies "
+                                 "\"legacy\". Using a SeedSequence requires "
                                  "mode=\"sequence\".")
-                mode = "sequence"
         elif mode is None and seed is not None:
             mode="sequence"
         self.mode = mode.lower() if mode is not None else "sequence"

randomgen/src/pcg64/pcg64-common.c

@@ -29,8 +29,7 @@ pcg128_t pcg_advance_lcg_128(pcg128_t state, pcg128_t delta, pcg128_t cur_mult,
         }
         cur_plus = pcg128_mult(pcg128_add(cur_mult, PCG_128BIT_CONSTANT(0u, 1u)), cur_plus);
         cur_mult = pcg128_mult(cur_mult, cur_mult);
-        delta.low >>= 1;
-        delta.low += delta.high & 1;
+        delta.low = (delta.low >> 1) | (delta.high << 63);
         delta.high >>= 1;
     }
     return pcg128_add(pcg128_mult(acc_mult, state), acc_plus);

randomgen/src/pcg64/pcg64.c

@@ -97,8 +97,7 @@ pcg128_t pcg_advance_lcg_128(pcg128_t state, pcg128_t delta, pcg128_t cur_mult,
         }
         cur_plus = pcg128_mult(pcg128_add(cur_mult, PCG_128BIT_CONSTANT(0u, 1u)), cur_plus);
         cur_mult = pcg128_mult(cur_mult, cur_mult);
-        delta.low >>= 1;
-        delta.low += delta.high & 1;
+        delta.low = (delta.low >> 1) | (delta.high << 63);
         delta.high >>= 1;
     }
     return pcg128_add(pcg128_mult(acc_mult, state), acc_plus);

randomgen/tests/test_direct.py

@@ -802,6 +802,8 @@ def setup_class(cls):
             (-2,),
             (2 ** 129 + 1,),
         ]
+        cls.large_advance_initial = 141078743063826365544432622475512570578
+        cls.large_advance_final = 32639015182640331666105117402520879107
 
     def setup_bitgenerator(self, seed, mode="legacy", inc: Optional[int] = 0):
         return self.bit_generator(*seed, mode=mode, variant="xsl-rr", inc=inc)  # type: ignore
@@ -861,6 +863,14 @@ def test_unknown_variant(self):
         with pytest.raises(ValueError):
             PCG64(0, variant=3)
 
+    def test_large_advance(self):
+        bg = self.setup_bitgenerator([0], inc=1)
+        state = bg.state["state"]
+        assert state["state"] == self.large_advance_initial
+        bg.advance(sum(2 ** i for i in range(96)))
+        state = bg.state["state"]
+        assert state["state"] == self.large_advance_final
+
 
 class TestPhilox(Random123):
     @classmethod
@@ -1354,6 +1364,8 @@ def setup_class(cls):
             (None, -1),
             (None, 2 ** 129 + 1),
         ]
+        cls.large_advance_initial = 645664597830827402
+        cls.large_advance_final = 3
 
     def setup_bitgenerator(self, seed, mode="legacy", inc=0):
         return self.bit_generator(*seed, mode=mode, inc=inc)
@@ -1948,10 +1960,20 @@ def setup_class(cls):
         else:
             cls.invalid_seed_values += [("apple",)]
         cls.seed_sequence_only = True
+        cls.large_advance_initial = 262626489767919729675955844831248137855
+        cls.large_advance_final = 326675794918500479020985263602132957772
 
     def setup_bitgenerator(self, seed, mode=None, inc=0):
         return self.bit_generator(*seed, inc=inc)
 
+    def test_large_advance(self):
+        bg = self.setup_bitgenerator([0], inc=1)
+        state = bg.state["state"]
+        assert state["state"] == self.large_advance_initial
+        bg.advance(sum(2 ** i for i in range(96)))
+        state = bg.state["state"]
+        assert state["state"] == self.large_advance_final
+
 
 class TestPCG64CMDXSM(TestPCG64DXSM):
     @classmethod
@@ -1960,6 +1982,8 @@ def setup_class(cls):
         cls.bit_generator = partial(PCG64, mode="sequence", variant="dxsm")
         cls.data1 = cls._read_csv(join(pwd, "./data/pcg64-cm-dxsm-testset-1.csv"))
         cls.data2 = cls._read_csv(join(pwd, "./data/pcg64-cm-dxsm-testset-2.csv"))
+        cls.large_advance_initial = 159934576226003702342121456273047082943
+        cls.large_advance_final = 43406923282132296644520456716700203596
 
 
 class TestEFIIX64(TestLXM):

setup.cfg

@@ -1,5 +1,5 @@
 [metadata]
-description-file = README.md
+description_file = README.md
 license_file = LICENSE.md
 
 [flake8]