Some important math constants are M_PI, M_PI_2, M_PI_4.
#define M_E 2.71828182845904523536028747135266250 /* e */
#define M_LOG2E 1.44269504088896340735992468100189214 /* log2(e) */
#define M_LOG10E 0.434294481903251827651128918916605082 /* log10(e) */
#define M_LN2 0.693147180559945309417232121458176568 /* loge(2) */
#define M_LN10 2.30258509299404568401799145468436421 /* loge(10) */
#define M_PI 3.14159265358979323846264338327950288 /* pi */
#define M_PI_2 1.57079632679489661923132169163975144 /* pi/2 */
#define M_PI_4 0.785398163397448309615660845819875721 /* pi/4 */
#define M_1_PI 0.318309886183790671537767526745028724 /* 1/pi */
#define M_2_PI 0.636619772367581343075535053490057448 /* 2/pi */
#define M_2_SQRTPI 1.12837916709551257389615890312154517 /* 2/sqrt(pi) */
#define M_SQRT2 1.41421356237309504880168872420969808 /* sqrt(2) */
#define M_SQRT1_2 0.707106781186547524400844362104849039 /* 1/sqrt(2) */
#define MAXFLOAT 0x1.fffffep+127f
