Tweaking.

include/fast_float/decimal_to_binary.h

@@ -43,15 +43,21 @@ value128 compute_product_approximation(int64_t q, uint64_t w) {
 
 namespace {
 /**
- * For q in (-400,350), we have that
+ * For q in (0,350), we have that
  *  f = (((152170 + 65536) * q ) >> 16);
  * is equal to
  *   floor(p) + q
  * where
  *   p = log(5**q)/log(2) = q * log(5)/log(2)
  *
+ * For negative values of q in (-400,0), we have that 
+ *  f = (((152170 + 65536) * q ) >> 16);
+ * is equal to 
+ *   -ceil(p) + q
+ * where
+ *   p = log(5**-q)/log(2) = -q * log(5)/log(2)
  */
-  fastfloat_really_inline unsigned int power(int q)  noexcept  {
+  fastfloat_really_inline int power(int q)  noexcept  {
     return (((152170 + 65536) * q) >> 16) + 63;
   }
 } // namespace
@@ -102,8 +108,12 @@ adjusted_mantissa compute_float(int64_t q, uint64_t w)  noexcept  {
 
   answer.mantissa = product.high >> (upperbit + 64 - binary::mantissa_explicit_bits() - 3);
   lz += int(1 ^ upperbit);
+  
   answer.power2 = power(int(q)) - lz - binary::minimum_exponent() + 1;
-
+//if(q < 0) {
+//  std::cout << "power(int("<< q << " )) = " << int(power(int(q))) << std::endl;
+//    std::cout << "result answer.power2  = " << answer.power2  << std::endl;
+//}
   if (answer.power2 <= 0) { // we have a subnormal?
     // Here have that answer.power2 <= 0 so -answer.power2 >= 0
     if(-answer.power2 + 1 >= 64) { // if we have more than 64 bits below the minimum exponent, you have a zero for sure.

tests/basictest.cpp

@@ -224,9 +224,114 @@ bool test_fixed_only() {
 }
 
 
+  static const double testing_power_of_ten[] = {
+      1e-307, 1e-306, 1e-305, 1e-304, 1e-303, 1e-302, 1e-301, 1e-300, 1e-299,
+      1e-298, 1e-297, 1e-296, 1e-295, 1e-294, 1e-293, 1e-292, 1e-291, 1e-290,
+      1e-289, 1e-288, 1e-287, 1e-286, 1e-285, 1e-284, 1e-283, 1e-282, 1e-281,
+      1e-280, 1e-279, 1e-278, 1e-277, 1e-276, 1e-275, 1e-274, 1e-273, 1e-272,
+      1e-271, 1e-270, 1e-269, 1e-268, 1e-267, 1e-266, 1e-265, 1e-264, 1e-263,
+      1e-262, 1e-261, 1e-260, 1e-259, 1e-258, 1e-257, 1e-256, 1e-255, 1e-254,
+      1e-253, 1e-252, 1e-251, 1e-250, 1e-249, 1e-248, 1e-247, 1e-246, 1e-245,
+      1e-244, 1e-243, 1e-242, 1e-241, 1e-240, 1e-239, 1e-238, 1e-237, 1e-236,
+      1e-235, 1e-234, 1e-233, 1e-232, 1e-231, 1e-230, 1e-229, 1e-228, 1e-227,
+      1e-226, 1e-225, 1e-224, 1e-223, 1e-222, 1e-221, 1e-220, 1e-219, 1e-218,
+      1e-217, 1e-216, 1e-215, 1e-214, 1e-213, 1e-212, 1e-211, 1e-210, 1e-209,
+      1e-208, 1e-207, 1e-206, 1e-205, 1e-204, 1e-203, 1e-202, 1e-201, 1e-200,
+      1e-199, 1e-198, 1e-197, 1e-196, 1e-195, 1e-194, 1e-193, 1e-192, 1e-191,
+      1e-190, 1e-189, 1e-188, 1e-187, 1e-186, 1e-185, 1e-184, 1e-183, 1e-182,
+      1e-181, 1e-180, 1e-179, 1e-178, 1e-177, 1e-176, 1e-175, 1e-174, 1e-173,
+      1e-172, 1e-171, 1e-170, 1e-169, 1e-168, 1e-167, 1e-166, 1e-165, 1e-164,
+      1e-163, 1e-162, 1e-161, 1e-160, 1e-159, 1e-158, 1e-157, 1e-156, 1e-155,
+      1e-154, 1e-153, 1e-152, 1e-151, 1e-150, 1e-149, 1e-148, 1e-147, 1e-146,
+      1e-145, 1e-144, 1e-143, 1e-142, 1e-141, 1e-140, 1e-139, 1e-138, 1e-137,
+      1e-136, 1e-135, 1e-134, 1e-133, 1e-132, 1e-131, 1e-130, 1e-129, 1e-128,
+      1e-127, 1e-126, 1e-125, 1e-124, 1e-123, 1e-122, 1e-121, 1e-120, 1e-119,
+      1e-118, 1e-117, 1e-116, 1e-115, 1e-114, 1e-113, 1e-112, 1e-111, 1e-110,
+      1e-109, 1e-108, 1e-107, 1e-106, 1e-105, 1e-104, 1e-103, 1e-102, 1e-101,
+      1e-100, 1e-99,  1e-98,  1e-97,  1e-96,  1e-95,  1e-94,  1e-93,  1e-92,
+      1e-91,  1e-90,  1e-89,  1e-88,  1e-87,  1e-86,  1e-85,  1e-84,  1e-83,
+      1e-82,  1e-81,  1e-80,  1e-79,  1e-78,  1e-77,  1e-76,  1e-75,  1e-74,
+      1e-73,  1e-72,  1e-71,  1e-70,  1e-69,  1e-68,  1e-67,  1e-66,  1e-65,
+      1e-64,  1e-63,  1e-62,  1e-61,  1e-60,  1e-59,  1e-58,  1e-57,  1e-56,
+      1e-55,  1e-54,  1e-53,  1e-52,  1e-51,  1e-50,  1e-49,  1e-48,  1e-47,
+      1e-46,  1e-45,  1e-44,  1e-43,  1e-42,  1e-41,  1e-40,  1e-39,  1e-38,
+      1e-37,  1e-36,  1e-35,  1e-34,  1e-33,  1e-32,  1e-31,  1e-30,  1e-29,
+      1e-28,  1e-27,  1e-26,  1e-25,  1e-24,  1e-23,  1e-22,  1e-21,  1e-20,
+      1e-19,  1e-18,  1e-17,  1e-16,  1e-15,  1e-14,  1e-13,  1e-12,  1e-11,
+      1e-10,  1e-9,   1e-8,   1e-7,   1e-6,   1e-5,   1e-4,   1e-3,   1e-2,
+      1e-1,   1e0,    1e1,    1e2,    1e3,    1e4,    1e5,    1e6,    1e7,
+      1e8,    1e9,    1e10,   1e11,   1e12,   1e13,   1e14,   1e15,   1e16,
+      1e17,   1e18,   1e19,   1e20,   1e21,   1e22,   1e23,   1e24,   1e25,
+      1e26,   1e27,   1e28,   1e29,   1e30,   1e31,   1e32,   1e33,   1e34,
+      1e35,   1e36,   1e37,   1e38,   1e39,   1e40,   1e41,   1e42,   1e43,
+      1e44,   1e45,   1e46,   1e47,   1e48,   1e49,   1e50,   1e51,   1e52,
+      1e53,   1e54,   1e55,   1e56,   1e57,   1e58,   1e59,   1e60,   1e61,
+      1e62,   1e63,   1e64,   1e65,   1e66,   1e67,   1e68,   1e69,   1e70,
+      1e71,   1e72,   1e73,   1e74,   1e75,   1e76,   1e77,   1e78,   1e79,
+      1e80,   1e81,   1e82,   1e83,   1e84,   1e85,   1e86,   1e87,   1e88,
+      1e89,   1e90,   1e91,   1e92,   1e93,   1e94,   1e95,   1e96,   1e97,
+      1e98,   1e99,   1e100,  1e101,  1e102,  1e103,  1e104,  1e105,  1e106,
+      1e107,  1e108,  1e109,  1e110,  1e111,  1e112,  1e113,  1e114,  1e115,
+      1e116,  1e117,  1e118,  1e119,  1e120,  1e121,  1e122,  1e123,  1e124,
+      1e125,  1e126,  1e127,  1e128,  1e129,  1e130,  1e131,  1e132,  1e133,
+      1e134,  1e135,  1e136,  1e137,  1e138,  1e139,  1e140,  1e141,  1e142,
+      1e143,  1e144,  1e145,  1e146,  1e147,  1e148,  1e149,  1e150,  1e151,
+      1e152,  1e153,  1e154,  1e155,  1e156,  1e157,  1e158,  1e159,  1e160,
+      1e161,  1e162,  1e163,  1e164,  1e165,  1e166,  1e167,  1e168,  1e169,
+      1e170,  1e171,  1e172,  1e173,  1e174,  1e175,  1e176,  1e177,  1e178,
+      1e179,  1e180,  1e181,  1e182,  1e183,  1e184,  1e185,  1e186,  1e187,
+      1e188,  1e189,  1e190,  1e191,  1e192,  1e193,  1e194,  1e195,  1e196,
+      1e197,  1e198,  1e199,  1e200,  1e201,  1e202,  1e203,  1e204,  1e205,
+      1e206,  1e207,  1e208,  1e209,  1e210,  1e211,  1e212,  1e213,  1e214,
+      1e215,  1e216,  1e217,  1e218,  1e219,  1e220,  1e221,  1e222,  1e223,
+      1e224,  1e225,  1e226,  1e227,  1e228,  1e229,  1e230,  1e231,  1e232,
+      1e233,  1e234,  1e235,  1e236,  1e237,  1e238,  1e239,  1e240,  1e241,
+      1e242,  1e243,  1e244,  1e245,  1e246,  1e247,  1e248,  1e249,  1e250,
+      1e251,  1e252,  1e253,  1e254,  1e255,  1e256,  1e257,  1e258,  1e259,
+      1e260,  1e261,  1e262,  1e263,  1e264,  1e265,  1e266,  1e267,  1e268,
+      1e269,  1e270,  1e271,  1e272,  1e273,  1e274,  1e275,  1e276,  1e277,
+      1e278,  1e279,  1e280,  1e281,  1e282,  1e283,  1e284,  1e285,  1e286,
+      1e287,  1e288,  1e289,  1e290,  1e291,  1e292,  1e293,  1e294,  1e295,
+      1e296,  1e297,  1e298,  1e299,  1e300,  1e301,  1e302,  1e303,  1e304,
+      1e305,  1e306,  1e307,  1e308};
+
+
+
+  bool powers_of_ten() {
+    std::cout << __func__ << std::endl;
+    char buf[1024];
+
+    bool is_pow_correct{1e-308 == std::pow(10,-308)};
+    int start_point = is_pow_correct ? -1000 : -307;
+    if(!is_pow_correct) {
+      std::cout << "On your system, the pow function is busted. Sorry about that. " << std::endl;
+    }
+    for (int i = start_point; i <= 308; ++i) {// large negative values should be zero.
+      std::cout << ".";
+      std::cout.flush();
+      size_t n = snprintf(buf, sizeof(buf), "1e%d", i);
+      if (n >= sizeof(buf)) { abort(); }
+      double actual;
+      auto result = fast_float::from_chars(buf, buf + 1000, actual);
+      if (result.ec != std::errc()) {
+       std::cerr << " I could not parse " << buf << std::endl;
+       return false;
+      }
+      double expected = ((i >= -307) ? testing_power_of_ten[i + 307]: std::pow(10, i));
+      if(actual!=expected) {
+        std::cerr << "String '" << buf << " parsed to " << actual;
+        return false;
+      }
+    }
+    std::cout << std::endl;
+    std::cout << "Powers of 10 can be parsed exactly.\n";
+    return true;
+  }
+
 int main() {
   Assert(test_fixed_only());
   Assert(test_scientific_only());
+  Assert(issue8());
   Assert(issue19());
   Assert(check_behavior());
   std::cout << "======= 64 bits " << std::endl;
@@ -372,7 +477,7 @@ int main() {
   Assert(basic_test_32bit("0.00000000000000000000000000000000000001175494210692441075487029444849287348827052428745893333857174530571588870475618904265502351336181163787841796875", 0.00000000000000000000000000000000000001175494210692441075487029444849287348827052428745893333857174530571588870475618904265502351336181163787841796875));
   std::cout << std::endl;
 
-  Assert(issue8());
+  Assert(powers_of_ten());
 
   std::cout << "All ok" << std::endl;
   return EXIT_SUCCESS;