Add cached powers of 10

support/compute-powers.py

@@ -8,9 +8,43 @@ min_exponent = -348
 max_exponent = 340
 step = 8
 significand_size = 64
-for exp in range(min_exponent, max_exponent + 1, step):
-    n = 10 ** exp if exp >= 0 else 2 ** 2000 / 10 ** -exp
+exp_offset = 2000
+
+class fp:
+    pass
+
+powers = []
+for i, exp in enumerate(range(min_exponent, max_exponent + 1, step)):
+    result = fp()
+    n = 10 ** exp if exp >= 0 else 2 ** exp_offset / 10 ** -exp
     k = significand_size + 1
     # Convert to binary and round.
-    n = (int('{:0<{}b}'.format(n, k)[:k], 2) + 1) / 2
-    print('{:0<#16x}ull'.format(n))
+    binary = '{:b}'.format(n)
+    result.f = (int('{:0<{}}'.format(binary[:k], k), 2) + 1) / 2
+    result.e = len(binary) - (exp_offset if exp < 0 else 0) - significand_size
+    powers.append(result)
+    # Sanity check.
+    exp_offset10 = 400
+    actual = result.f * 10 ** exp_offset10
+    if result.e > 0:
+        actual *= 2 ** result.e
+    else:
+        for j in range(-result.e):
+            actual /= 2
+    expected = 10 ** (exp_offset10 + exp)
+    precision = len('{}'.format(expected)) - len('{}'.format(actual - expected))
+    if precision < 19:
+        print('low precision:', precision)
+        exit(1)
+
+print('Significands:', end='')
+for i, fp in enumerate(powers):
+    if i % 3 == 0:
+        print(end='\n ')
+    print(' {:0<#16x}ull'.format(fp.f, ), end=',')
+
+print('\n\nExponents:', end='')
+for i, fp in enumerate(powers):
+    if i % 11 == 0:
+        print(end='\n ')
+    print(' {:5}'.format(fp.e), end=',')