Fix float precision loss in JSON serialization and cpool deduplication (issue #420)

Two root causes behind 'RUNTIME ERROR: Unknown LOADK index' on -c/-x path:

1. gravity_json.c: float constants were serialized with '%f' (6 decimal
   places), silently rounding small values like -0.000000004 to -0.000000.
   When two distinct floats rounded to the same string, one was dropped from
   the JSON pool, leaving the bytecode referencing a non-existent index.
   Fixed by switching to '%.17g' (17 significant digits, full IEEE 754
   double round-trip), with a '.0' suffix appended for whole-number values
   so they deserialize as float rather than integer.

2. gravity_value.c: gravity_function_cpool_add used the epsilon-based
   gravity_value_equals (EPSILON=1e-6) to detect duplicate constants.
   Any two floats differing by less than 1e-6 were merged into one cpool
   entry, causing index mismatches at runtime. The cpool now uses exact
   bit-level comparison (v.f != v2.f) for float values before falling back
   to the fuzzy equality check used for all other types.

Also fix run_all.sh to work on macOS where GNU 'timeout' is not available:
detect 'timeout', 'gtimeout' (brew coreutils), or fall back to a pure-bash
background kill-watcher that returns exit code 124 on expiry.

Author: marcobambini

src/shared/gravity_value.c

@@ -593,6 +593,14 @@ uint16_t gravity_function_cpool_add (gravity_vm *vm, gravity_function_t *f, grav
     size_t n = marray_size(f->cpool);
     for (size_t i=0; i<n; i++) {
         gravity_value_t v2 = marray_get(f->cpool, i);
+        // Float constants must match exactly at the bit level so that distinct
+        // small values (e.g. -4e-9 vs -5e-11) are never merged due to the
+        // epsilon-based gravity_value_equals comparison.
+        if (v.isa == gravity_class_float && v2.isa == gravity_class_float) {
+            if (v.f != v2.f) continue;
+            gravity_value_free(NULL, v);
+            return (uint16_t)i;
+        }
         if (gravity_value_equals(v,v2)) {
             gravity_value_free(NULL, v);
             return (uint16_t)i;

src/utils/gravity_json.c

@@ -299,8 +299,18 @@ void json_add_double (json_t *json, const char *key, double value) {
     json_check_comma(json);
 
     char buffer[512];
-    // was %g but we don't like scientific notation nor the missing .0 in case of float number with no decimals
-    size_t len = snprintf(buffer, sizeof(buffer), "%f", value);
+    // Use %.17g for a lossless double round-trip (17 significant digits covers
+    // the full IEEE 754 range without precision loss that occurred with "%f").
+    // If the result contains no decimal point or exponent, append ".0" so the
+    // value is deserialized as a float rather than an integer.
+    size_t len = snprintf(buffer, sizeof(buffer), "%.17g", value);
+    bool has_dot_or_exp = false;
+    for (size_t i = 0; i < len; i++) {
+        if (buffer[i] == '.' || buffer[i] == 'e' || buffer[i] == 'E') { has_dot_or_exp = true; break; }
+    }
+    if (!has_dot_or_exp && len + 2 < sizeof(buffer)) {
+        buffer[len++] = '.'; buffer[len++] = '0'; buffer[len] = '\0';
+    }
 
     if (key) {
         json_write_raw (json, key, strlen(key), true, true);

test/unittest/run_all.sh

@@ -10,6 +10,32 @@ set -u -o pipefail
 
 readonly SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
 readonly GRAVITY_BIN=$SCRIPT_DIR/../../gravity
+
+# Resolve a portable timeout implementation.
+# Preference order: timeout (Linux/GNU coreutils) → gtimeout (macOS + brew
+# install coreutils) → pure-bash fallback using a background kill watcher.
+if command -v timeout &>/dev/null; then
+    run_timeout() { timeout "$@"; }
+elif command -v gtimeout &>/dev/null; then
+    run_timeout() { gtimeout "$@"; }
+else
+    run_timeout() {
+        local t=$1; shift
+        "$@" &
+        local pid=$!
+        ( sleep "$t" && kill "$pid" 2>/dev/null ) &
+        local watcher=$!
+        wait "$pid" 2>/dev/null
+        local rc=$?
+        kill "$watcher" 2>/dev/null
+        wait "$watcher" 2>/dev/null
+        # If the process was killed by our watcher (SIGTERM = 143) mimic the
+        # standard timeout exit code of 124 so the caller can detect timeouts.
+        [[ $rc -eq 143 ]] && return 124
+        return $rc
+    }
+fi
+
 files=$(find $SCRIPT_DIR -iname "*.gravity" | grep -v disabled)
 tests_total=$(echo "$files" | wc -l)
 tests_success=0
@@ -24,7 +50,7 @@ for test in $files; do
     if [[ "$test" =~ "mem" || "$test" =~ "recursion" ]]; then
         timeout=10
     fi
-    timeout $timeout "$GRAVITY_BIN" "$test"
+    run_timeout $timeout "$GRAVITY_BIN" "$test"
     res=$?
     if [[ $res -eq 0 ]]; then
         tests_success=$(($tests_success+1))