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Improve speed of proof of matvec_mul() #408

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Nov 15, 2024
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Improve speed of proof of matvec_mul() #408

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73abc1a
Improve speed of proof of matvec_mul()
rod-chapman Nov 14, 2024
70b1d19
Add comments to explain the new settings for CBMCFLAGS.
rod-chapman Nov 14, 2024
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16 changes: 13 additions & 3 deletions cbmc/proofs/matvec_mul/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -13,20 +13,30 @@ DEFINES +=
INCLUDES +=

REMOVE_FUNCTION_BODY +=
UNWINDSET += matvec_mul.0:4 # Maximum value of MLKEM_K

PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
PROJECT_SOURCES += $(SRCDIR)/mlkem/indcpa.c

CHECK_FUNCTION_CONTRACTS=matvec_mul
USE_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)polyvec_mulcache_compute $(MLKEM_NAMESPACE)polyvec_basemul_acc_montgomery_cached
USE_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)polyvec_basemul_acc_montgomery_cached
APPLY_LOOP_CONTRACTS=on
USE_DYNAMIC_FRAMES=1

# Disable any setting of EXTERNAL_SAT_SOLVER, and choose SMT backend instead
EXTERNAL_SAT_SOLVER=
CBMCFLAGS=--smt2

# For this proof we tell CBMC to
# 1. not decompose arrays into their individual cells
# 2. to model arrays directly as SMT-lib arrays
# 3. to slice constraints that are not in the cone of influcence of the proof obligations
# These options simplify them modelling of arrays and produce much more compact
# SMT files, leaving all array-type reasoning to the SMT solver.
#
# For functions that use large and multi-dimensional arrays, this yields
# a substantial improvement in proof performance.
CBMCFLAGS += --no-array-field-sensitivity --arrays-uf-always --slice-formula

FUNCTION_NAME = $(MLKEM_NAMESPACE)matvec_mul

# If this proof is found to consume huge amounts of RAM, you can set the
Expand All @@ -36,7 +46,7 @@ FUNCTION_NAME = $(MLKEM_NAMESPACE)matvec_mul
# EXPENSIVE = true

# This function is large enough to need...
CBMC_OBJECT_BITS = 10
CBMC_OBJECT_BITS = 8

# If you require access to a file-local ("static") function or object to conduct
# your proof, set the following (and do not include the original source file
Expand Down
11 changes: 7 additions & 4 deletions mlkem/indcpa.c
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Expand Up @@ -220,7 +220,7 @@ void gen_matrix_entry(poly *entry,
while (ctr < MLKEM_N) // clang-format off
ASSIGNS(ctr, state, OBJECT_UPTO(entry, sizeof(poly)), OBJECT_WHOLE(buf))
INVARIANT(0 <= ctr && ctr <= MLKEM_N)
INVARIANT(ctr > 0 ==> ARRAY_BOUND(entry->coeffs, 0, ctr - 1,
INVARIANT(ctr > 0 ==> ARRAY_BOUND(entry->coeffs, 0, ctr - 1,
0, (MLKEM_Q - 1))) // clang-format on
{
shake128_squeezeblocks(buf, 1, &state);
Expand Down Expand Up @@ -342,9 +342,12 @@ void matvec_mul(polyvec *out, const polyvec a[MLKEM_K], const polyvec *v,
ASSIGNS(OBJECT_WHOLE(out))
// clang-format on
{
for (int i = 0; i < MLKEM_K; i++) {
polyvec_basemul_acc_montgomery_cached(&out->vec[i], &a[i], v, vc);
}
for (int i = 0; i < MLKEM_K; i++) // clang-format off
ASSIGNS(i, OBJECT_WHOLE(out))
INVARIANT(i >= 0 && i <= MLKEM_K) // clang-format on
{
polyvec_basemul_acc_montgomery_cached(&out->vec[i], &a[i], v, vc);
}
}

/*************************************************
Expand Down