Add 'missing' consts to math.zig

The C library defines constants for log2e and sqrt2 etc. Those should also be available in zig.

lib/std/math.zig

@@ -9,6 +9,17 @@ pub const e = 2.71828182845904523536028747135266249775724709369995;
 
 /// Archimedes' constant (π)
 pub const pi = 3.14159265358979323846264338327950288419716939937510;
+pub const log2e = 1.442695040888963407359924681001892137; // log2(e)
+pub const log10e = 0.434294481903251827651128918916605082; // log10(e)
+pub const ln2 = 0.693147180559945309417232121458176568; // ln(2)
+pub const ln10 = 2.302585092994045684017991454684364208; // ln(10)
+pub const pi_2 = 1.570796326794896619231321691639751442; // pi/2
+pub const pi_4 = 0.785398163397448309615660845819875721; // pi/4
+pub const one_pi = 0.318309886183790671537767526745028724; // 1/pi
+pub const two_pi = 0.636619772367581343075535053490057448; // 2/pi
+pub const two_sqrtpi = 1.128379167095512573896158903121545172; // 2/sqrt(pi)
+pub const sqrt2 = 1.414213562373095048801688724209698079; // sqrt(2)
+pub const sqrt1_2 = 0.707106781186547524400844362104849039; // 1/sqrt(2)
 
 // From a small c++ [program using boost float128](https://github.com/winksaville/cpp_boost_float128)
 pub const f128_true_min = @bitCast(f128, u128(0x00000000000000000000000000000001));