Use static tables rather than computing on startup.

Author: nascheme

Objects/longobject.c

@@ -2821,35 +2821,57 @@ just 1 digit at the start, so that the copying code was exercised for every
 digit beyond the first.
 ***/
 
-static double log_base_BASE[37] = {0.0e0,};
-static int convwidth_base[37] = {0,};
-static twodigits convmultmax_base[37] = {0,};
-
-static void
-long_precompute_base_conv(void)
-{
-    // These constants are quick to compute (likely less than 1 μs) and
-    // computing them at runtime avoids hard-coding a table dependant on
-    // PyLong_BASE.
-    for (int base = 2; base <= 36; base++) {
-        twodigits convmax = base;
-        int i = 1;
-
-        log_base_BASE[base] = (log((double)base) /
-                               log((double)PyLong_BASE));
-        for (;;) {
-            twodigits next = convmax * base;
-            if (next > PyLong_BASE) {
-                break;
-            }
-            convmax = next;
-            ++i;
-        }
-        convmultmax_base[base] = convmax;
-        assert(i > 0);
-        convwidth_base[base] = i;
-    }
-}
+// Tables are computed by Tools/scripts/long_conv_tables.py
+#if PYLONG_BITS_IN_DIGIT == 15
+    static double log_base_BASE[37] = {0.0, 0.0, 0.06666666666666667,
+        0.10566416671474375, 0.13333333333333333, 0.15479520632582416,
+        0.17233083338141042, 0.18715699480384027, 0.19999999999999998,
+        0.2113283334294875, 0.22146187299249084, 0.23062877457581984,
+        0.2389975000480771, 0.24669598120940617, 0.25382366147050694,
+        0.26045937304056793, 0.26666666666666666, 0.27249752275002265,
+        0.27799500009615413, 0.2831951675629057, 0.28812853965915747,
+        0.29282116151858406, 0.2972954412424865, 0.3015707970704675,
+        0.3056641667147438, 0.30959041265164833, 0.3133626478760728,
+        0.31699250014423125, 0.3204903281371736, 0.3238653996751715,
+        0.3271260397072346, 0.3302797540257917, 0.33333333333333337,
+        0.3362929412905636, 0.3391641894166893, 0.34195220112966446,
+        0.34466166676282084};
+    static int convmultmax_base[37] = {0, 0, 32768, 19683, 16384,
+        15625, 7776, 16807, 32768, 6561, 10000, 14641, 20736, 28561,
+        2744, 3375, 4096, 4913, 5832, 6859, 8000, 9261, 10648, 12167,
+        13824, 15625, 17576, 19683, 21952, 24389, 27000, 29791, 32768,
+        1089, 1156, 1225, 1296};
+    static twodigits convwidth_base[37] = {0, 0, 15, 9, 7, 6, 5, 5, 5,
+        4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+        3, 3, 3, 2, 2, 2, 2};
+#elif PYLONG_BITS_IN_DIGIT == 30
+    static double log_base_BASE[37] = {0.0, 0.0, 0.03333333333333333,
+        0.05283208335737188, 0.06666666666666667, 0.07739760316291208,
+        0.08616541669070521, 0.09357849740192013, 0.09999999999999999,
+        0.10566416671474375, 0.11073093649624542, 0.11531438728790992,
+        0.11949875002403855, 0.12334799060470308, 0.12691183073525347,
+        0.13022968652028397, 0.13333333333333333, 0.13624876137501132,
+        0.13899750004807707, 0.14159758378145285, 0.14406426982957873,
+        0.14641058075929203, 0.14864772062124326, 0.15078539853523376,
+        0.1528320833573719, 0.15479520632582416, 0.1566813239380364,
+        0.15849625007211562, 0.1602451640685868, 0.16193269983758574,
+        0.1635630198536173, 0.16513987701289584, 0.16666666666666669,
+        0.1681464706452818, 0.16958209470834465, 0.17097610056483223,
+        0.17233083338141042};
+    static int convmultmax_base[37] = {0, 0, 1073741824, 387420489,
+        1073741824, 244140625, 362797056, 282475249, 1073741824,
+        387420489, 1000000000, 214358881, 429981696, 815730721,
+        105413504, 170859375, 268435456, 410338673, 612220032,
+        893871739, 64000000, 85766121, 113379904, 148035889,
+        191102976, 244140625, 308915776, 387420489, 481890304,
+        594823321, 729000000, 887503681, 1073741824, 39135393,
+        45435424, 52521875, 60466176};
+    static twodigits convwidth_base[37] = {0, 0, 30, 18, 15, 12, 11,
+        10, 10, 9, 9, 8, 8, 8, 7, 7, 7, 7, 7, 7, 6, 6, 6, 6, 6, 6, 6,
+        6, 6, 6, 6, 6, 6, 5, 5, 5, 5};
+#else
+    #error "invalid PYLONG_BITS_IN_DIGIT value"
+#endif
 
 static int
 long_from_non_binary_base(const char *start, const char *end, Py_ssize_t digits, int base, PyLongObject **res)
@@ -2863,7 +2885,7 @@ long_from_non_binary_base(const char *start, const char *end, Py_ssize_t digits,
     PyLongObject *z;
     const char *p;
 
-    assert(log_base_BASE[base] != 0.0); // pre-computed by _PyLong_InitRuntime()
+    assert(log_base_BASE[base] != 0.0);
 
     /* Create an int object that can contain the largest possible
      * integer with this base and length.  Note that there's no
@@ -6750,13 +6772,6 @@ PyLong_GetInfo(void)
 
 /* runtime lifecycle */
 
-PyStatus
-_PyLong_InitRuntime(void)
-{
-    long_precompute_base_conv();
-    return _PyStatus_OK();
-}
-
 PyStatus
 _PyLong_InitTypes(PyInterpreterState *interp)
 {

Python/pylifecycle.c

@@ -510,11 +510,6 @@ pycore_init_runtime(_PyRuntimeState *runtime,
         return status;
     }
 
-    status = _PyLong_InitRuntime();
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
-
     status = _PyImport_Init();
     if (_PyStatus_EXCEPTION(status)) {
         return status;

Tools/scripts/long_conv_tables.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+#
+# Compute tables for longobject.c integer conversion.
+
+import math
+import textwrap
+
+
+def format_array(name, values):
+    values = [str(v) for v in values]
+    values = ', '.join(values)
+    result = f'{name} = {{{values}}};'
+    result = textwrap.wrap(
+        result,
+        initial_indent=' ' * 4,
+        subsequent_indent=' ' * 8,
+    )
+    return '\n'.join(result)
+
+
+def conv_tables(long_bits):
+    steps = 0
+    PyLong_BASE = 1 << long_bits
+    log_base_BASE = [0.0] * 37
+    convmultmax_base = [0] * 37
+    convwidth_base = [0] * 37
+    for base in range(2, 37):
+        convmax = base
+        i = 1
+        log_base_BASE[base] = math.log(float(base)) / math.log(PyLong_BASE)
+        while True:
+            steps += 1
+            next = convmax * base
+            if next > PyLong_BASE:
+                break
+            convmax = next
+            i += 1
+        convmultmax_base[base] = convmax
+        assert i > 0
+        convwidth_base[base] = i
+    # print('steps', steps)
+    return '\n'.join(
+        [
+            format_array('static double log_base_BASE[37]', log_base_BASE),
+            format_array('static int convmultmax_base[37]', convmultmax_base),
+            format_array(
+                'static twodigits convwidth_base[37]', convwidth_base
+            ),
+        ]
+    )
+
+
+def main():
+    print(
+        f'''\
+// Tables are computed by Tools/scripts/long_conv_tables.py
+#if PYLONG_BITS_IN_DIGIT == 15
+{conv_tables(15)}
+#elif PYLONG_BITS_IN_DIGIT == 30
+{conv_tables(30)}
+#else
+    #error "invalid PYLONG_BITS_IN_DIGIT value"
+#endif
+'''
+    )
+
+
+if __name__ == '__main__':
+    main()