feat: add fp-stability command for Verrou-based FP instability testing

.github/workflows/fp-stability.yml

@@ -0,0 +1,78 @@
+name: FP Stability
+
+# Runs the Verrou-based floating-point stability suite.
+#
+# What it tests (./mfc.sh fp-stability):
+#   sod_strong       1-D Sod shock, p_L/p_R=100,000, ideal gas
+#                    25 cells, 5 steps, WENO5 + HLLC
+#                    Compares density & energy vs. threshold 1e-10
+#                    Probes: HLLC xi-factor cancellation near sonic contact
+#                            (s_L - vel_L)/(s_L - s_S) when s_L ≈ s_S
+#
+#   water_stiffened  1-D water shock, stiffened EOS (pi_inf=4046)
+#                    25 cells, 5 steps, WENO5 + HLLC
+#                    Compares density & pressure vs. threshold 1e-10
+#                    Probes: pressure-recovery cancellation p=(E-pi_inf)/gamma
+#                            loses ~4 decimal digits when pi_inf/p_right ~ 40,000
+#
+# For each case: 1 nearest-rounding reference run + N random-rounding runs.
+# PASS if max L∞ deviation across all N samples stays below threshold.
+#
+# Verrou (Valgrind 3.26.0 + edf-hpc/verrou@a58d434) is built once and cached.
+# Build takes ~20 min uncached; cached runs restore in ~30 s.
+
+on:
+  push:
+  workflow_dispatch:
+
+jobs:
+  fp-stability:
+    name: Floating-Point Stability (Verrou)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Clone
+        uses: actions/checkout@v4
+
+      - name: Cache Verrou
+        id: cache-verrou
+        uses: actions/cache@v4
+        with:
+          path: ~/.local/verrou
+          key: verrou-a58d434-valgrind-3.26.0-${{ runner.os }}
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y \
+            build-essential automake python3 libc6-dbg \
+            cmake gfortran
+
+      - name: Build Verrou
+        if: steps.cache-verrou.outputs.cache-hit != 'true'
+        run: |
+          cd /tmp
+          wget -q https://sourceware.org/pub/valgrind/valgrind-3.26.0.tar.bz2
+          tar xf valgrind-3.26.0.tar.bz2
+
+          git clone https://github.com/edf-hpc/verrou.git
+          git -C verrou checkout a58d434
+
+          # Merge Verrou into Valgrind source tree and patch
+          cp -r verrou valgrind-3.26.0/verrou
+          cd valgrind-3.26.0
+          cat verrou/valgrind.*diff | patch -p1
+
+          ./autogen.sh
+          ./configure --enable-only64bit --prefix="$HOME/.local/verrou"
+          make -j"$(nproc)"
+          make install
+
+      - name: Verify Verrou
+        run: ~/.local/verrou/bin/valgrind --version
+
+      - name: Build MFC (debug, serial)
+        run: ./mfc.sh build -t pre_process simulation --no-mpi --debug -j"$(nproc)"
+
+      - name: Run FP Stability Suite
+        run: ./mfc.sh fp-stability -N 5

.gitignore

@@ -37,6 +37,7 @@ docs/documentation/parameters.md
 /tests/*/**
 !/tests/*/golden.txt
 !/tests/*/golden-metadata.txt
+!/tests/fp_stability/**
 
 # NVIDIA Nsight Compute
 *.nsys-rep

toolchain/main.py

@@ -198,6 +198,10 @@ def __run():
         from mfc import params_cmd
 
         params_cmd.params()
+    elif cmd == "fp-stability":
+        from mfc import fp_stability
+
+        fp_stability.fp_stability()
 
 
 if __name__ == "__main__":

toolchain/mfc/cli/commands.py

@@ -900,6 +900,65 @@
     include_common=["targets", "mfc_config", "jobs", "verbose", "debug_log"],
 )
 
+FP_STABILITY_COMMAND = Command(
+    name="fp-stability",
+    help="Run floating-point stability tests using Verrou.",
+    description=(
+        "Runs each registered test case N times under Verrou's random IEEE-754 "
+        "rounding mode and compares against a nearest-rounding reference run.  "
+        "Reports the max L∞ deviation and PASS/FAIL against per-case thresholds.\n\n"
+        "Requires a Verrou-enabled Valgrind at $VERROU_HOME/bin/valgrind "
+        "(defaults to $HOME/.local/verrou).  The simulation and pre_process "
+        "binaries must be serial (no-MPI, no-GPU) debug builds.\n\n"
+        "Current test cases:\n"
+        "  sod_strong      1-D Sod p_L/p_R=100,000 — HLLC xi-factor cancellation\n"
+        "  water_stiffened 1-D water shock (pi_inf=4046) — pressure-recovery cancellation\n"
+    ),
+    include_common=["mfc_config", "verbose", "debug_log"],
+    arguments=[
+        Argument(
+            name="sim-binary",
+            help="Path to a serial simulation binary (debug, no-MPI). Auto-discovered from build/install/ if omitted.",
+            default=None,
+            metavar="PATH",
+        ),
+        Argument(
+            name="pre-binary",
+            help="Path to a serial pre_process binary (no-MPI). Auto-discovered from build/install/ if omitted.",
+            default=None,
+            metavar="PATH",
+        ),
+        Argument(
+            name="verrou-binary",
+            help="Path to a Verrou-enabled valgrind binary. Defaults to $VERROU_HOME/bin/valgrind or $HOME/.local/verrou/bin/valgrind.",
+            default=None,
+            metavar="PATH",
+        ),
+        Argument(
+            name="samples",
+            short="N",
+            help="Number of random-rounding simulation runs per test case.",
+            type=int,
+            default=5,
+            metavar="N",
+        ),
+    ],
+    examples=[
+        Example("./mfc.sh fp-stability", "Auto-discover binaries and run all cases"),
+        Example(
+            "./mfc.sh fp-stability --sim-binary build/install/abc123/bin/simulation",
+            "Specify simulation binary explicitly",
+        ),
+        Example("./mfc.sh fp-stability -N 10", "Run 10 random-rounding samples per case"),
+    ],
+    key_options=[
+        ("--sim-binary PATH", "Serial simulation binary (debug, no-MPI)"),
+        ("--pre-binary PATH", "Serial pre_process binary"),
+        ("--verrou-binary PATH", "Verrou-enabled valgrind"),
+        ("-N, --samples N", "Random-rounding samples per case (default: 5)"),
+    ],
+)
+
 VIZ_COMMAND = Command(
     name="viz",
     help="Visualize post-processed MFC output.",
@@ -1372,6 +1431,7 @@
         BENCH_DIFF_COMMAND,
         COUNT_COMMAND,
         COUNT_DIFF_COMMAND,
+        FP_STABILITY_COMMAND,
     ],
     common_sets=[
         COMMON_TARGETS,