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Fix bit_length=64 undefined behavior, make it configurable, and lower --samples/--max_nb defaults #12

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Merged
hfwen0502 merged 3 commits into from
Sep 1, 2026
Merged

Fix bit_length=64 undefined behavior, make it configurable, and lower --samples/--max_nb defaults #12

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b772e21
Fix undefined behavior from hardcoded bit_length=64; make it configur…
hfwen0502 Sep 1, 2026
e38a642
Lower --samples default to 3000 and --max_nb default to 10
hfwen0502 Sep 1, 2026
147196c
Update example notebook to bit_length 20
hfwen0502 Sep 1, 2026
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2 changes: 1 addition & 1 deletion python/examples/run_sqd_sbd.ipynb
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Original file line number Diff line number Diff line change
Expand Up @@ -199,7 +199,7 @@
" 'carryover_type': 1, # singles-only carryover (stable default)\n",
" 'ratio': 0.1,\n",
" 'threshold': 1e-4,\n",
" 'bit_length': 64,\n",
" 'bit_length': 20, # bits per size_t; RIKEN default (64 is UB in bitadvance)\n",
" # serial: 1×1×1 MPI sub-communicator grid\n",
" 'adet_comm_size': 1, 'bdet_comm_size': 1, 'task_comm_size': 1,\n",
"}\n",
Expand Down
10 changes: 7 additions & 3 deletions python/examples/run_sqd_sbd.py
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Expand Up @@ -65,7 +65,7 @@ def parse_args():
p.add_argument("--fcidump", required=True, help="Path to FCIDUMP file")
p.add_argument("--counts", default=None,
help="Path to count_dict.json (bitstring counts from hardware)")
p.add_argument("--samples", type=int, default=10000,
p.add_argument("--samples", type=int, default=3000,
help="Number of uniform random samples (used when --counts is not given)")
p.add_argument("--device",
choices=["auto", "cpu", "gpu", "gpu-omp", "gpu-nvidia-omp"],
Expand All @@ -85,13 +85,17 @@ def parse_args():
p.add_argument("--tolerance", "--eps", type=float, default=1e-8, dest="eps")
p.add_argument("--iteration", "--max_it", type=int, default=100, dest="max_it",
help="Max SBD Davidson iterations per diagonalization")
p.add_argument("--block", "--max_nb", type=int, default=50, dest="max_nb")
p.add_argument("--block", "--max_nb", type=int, default=10, dest="max_nb")
p.add_argument("--rdm", "--do_rdm", type=int, default=0, dest="do_rdm",
help="0=density only (default, sufficient for SQD), 1=full RDM")
p.add_argument("--shuffle", "--do_shuffle", type=int, default=0, dest="do_shuffle")
p.add_argument("--carryover_type", type=int, default=1)
p.add_argument("--carryover_ratio", "--ratio", type=float, default=0.1, dest="ratio")
p.add_argument("--carryover_threshold", "--threshold", type=float, default=1e-4, dest="threshold")
p.add_argument("--bit_length", type=int, default=20,
help="Bits packed into each size_t of the bitstring representation "
"(RIKEN default 20). Must be <= 63: bitadvance() shifts a "
"64-bit size_t by this amount, so 64 is undefined behavior.")

# MPI sub-communicator sizes
p.add_argument("--adet_comm_size", type=int, default=1)
Expand Down Expand Up @@ -223,7 +227,7 @@ def main():
"carryover_type": args.carryover_type,
"ratio": args.ratio,
"threshold": args.threshold,
"bit_length": 64,
"bit_length": args.bit_length,
"adet_comm_size": args.adet_comm_size,
"bdet_comm_size": args.bdet_comm_size,
"task_comm_size": args.task_comm_size,
Expand Down
37 changes: 28 additions & 9 deletions python/sbd_solver.py
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Expand Up @@ -29,6 +29,17 @@
import numpy as np
from mpi4py import MPI

# Bits packed into each size_t of SBD's ``std::vector<size_t>`` bitstring
# representation. RIKEN's documented default is 20 (see the --bit_length option
# in apps/chemistry_tpb_selected_basis_diagonalization/README.md), which is also
# what run_sbd_diag.py defaults to.
#
# This must stay <= 63. bitadvance() in framework/bit_manipulation.h computes
# size_t d = (((size_t) 1) << bit_length) - 1;
# so bit_length == 64 shifts a 64-bit size_t by 64, which is undefined behavior;
# in practice the shift count is masked to 0 and the mask collapses to d == 0.
SBD_DEFAULT_BIT_LENGTH = 20

try:
from pyscf import tools as pyscf_tools
except ImportError:
Expand Down Expand Up @@ -154,11 +165,15 @@ def _solve_sci_core(
the FCIDUMP only once and reuse it across all batches.
"""
strings_a, strings_b = ci_strings
adet = _ci_strings_to_sbd_dets(strings_a, norb, backend)
bdet = _ci_strings_to_sbd_dets(strings_b, norb, backend)

# Build the config first: it carries the effective bit_length (possibly
# overridden by the caller), and the determinants must be packed with the
# same value the C++ engine will use to interpret them.
sbd_data = _create_sbd_config(sbd_config, backend, device_config)

adet = _ci_strings_to_sbd_dets(strings_a, norb, backend, sbd_data.bit_length)
bdet = _ci_strings_to_sbd_dets(strings_b, norb, backend, sbd_data.bit_length)

# Use .bin extension to trigger SBD's fast binary write path
# (SaveMatrixFormWF in restart.h checks extension: .bin -> raw doubles)
wf_dump_file = sbd_dir / "wavefunction.bin"
Expand Down Expand Up @@ -199,8 +214,12 @@ def _solve_sci_core(
occupancies_b = density[1::2]
occupancies = (occupancies_a, occupancies_b)

co_strings_a = _sbd_dets_to_ci_strings(results["carryover_adet"], norb, backend)
co_strings_b = _sbd_dets_to_ci_strings(results["carryover_bdet"], norb, backend)
co_strings_a = _sbd_dets_to_ci_strings(
results["carryover_adet"], norb, backend, sbd_data.bit_length
)
co_strings_b = _sbd_dets_to_ci_strings(
results["carryover_bdet"], norb, backend, sbd_data.bit_length
)

# Read wavefunction coefficients from binary dump
n_alpha_co = len(co_strings_a)
Expand Down Expand Up @@ -411,14 +430,14 @@ def _read_fcidump_ecore(fcidump_path):


def _ci_strings_to_sbd_dets(
ci_strings: np.ndarray, norb: int, backend
ci_strings: np.ndarray, norb: int, backend,
bit_length: int = SBD_DEFAULT_BIT_LENGTH,
) -> list[list[int]]:
"""Convert CI strings (integers) to SBD determinant format.

Determinants are sorted in canonical order (matching C++ sort_bitarray)
which is required by the GPU Correlation kernel (do_rdm=1).
"""
bit_length = 64
dets = []
for ci_str in ci_strings:
binary_str = format(int(ci_str), f'0{norb}b')
Expand All @@ -428,10 +447,10 @@ def _ci_strings_to_sbd_dets(


def _sbd_dets_to_ci_strings(
dets: list[list[int]], norb: int, backend
dets: list[list[int]], norb: int, backend,
bit_length: int = SBD_DEFAULT_BIT_LENGTH,
) -> np.ndarray:
"""Convert SBD determinants to CI strings (integers)."""
bit_length = 64
ci_strings = []
for det in dets:
binary_str = backend.makestring(det, bit_length, norb)
Expand Down Expand Up @@ -459,7 +478,7 @@ def _create_sbd_config(config_dict: dict | None = None, backend=None, device_con
sbd_data.carryover_type = 1
sbd_data.ratio = 0.1
sbd_data.threshold = 1e-4
sbd_data.bit_length = 64
sbd_data.bit_length = SBD_DEFAULT_BIT_LENGTH

if config_dict:
for key, value in config_dict.items():
Expand Down