added math sqrt test with instructions

Author: ValRCS

src/sqrt_test.c

@@ -0,0 +1,66 @@
+#include <errno.h>
+#include <fenv.h>
+#include <math.h>
+#include <stdio.h>
+
+// Compilation instructions!
+// for compiling math you need add -lm at the very end!
+// 1. The C Standard vs. Implementations
+
+// The C standard (ISO/IEC 9899) says that functions like sqrt, sin, log,
+// feclearexcept, etc. exist in the library.
+
+// But the standard doesn’t say how they must be organized in the actual runtime
+// system.
+
+// Compiler vendors (like GCC on Unix) are free to put them in a separate
+// library (libm) instead of the default libc.
+
+// 2. Why Split into libc and libm?
+
+// Historical reason (Unix in the 1970s):
+
+// Early C programs often didn’t need floating-point math (think of simple
+// utilities and text processing).
+
+// Floating-point math routines were large and sometimes required special
+// hardware support (math co-processors).
+
+// To avoid bloating every program, they were separated into libm.
+
+// That way, only programs that actually needed math functions had to pay the
+// cost of linking libm.
+
+// 3. GCC Linking Rules
+
+// By default, gcc file.c -o prog links libc, because every C program needs
+// basic functions (printf, malloc, etc.).
+
+// But it does not link libm unless you explicitly request it with -lm.
+
+// Linker order matters:
+
+// gcc file.c -lm -o prog   # works
+// gcc -lm file.c -o prog   # usually fails
+
+// because the linker only searches libraries after seeing unresolved
+// references.
+
+// #pragma STDC FENV_ACCESS ON
+
+int main(void) {
+  printf("sqrt(100) = %f\n", sqrt(100));
+
+  printf("sqrt(-1.0) = %f\n", sqrt(-1.0));
+
+  errno = 0;
+  feclearexcept(FE_ALL_EXCEPT);
+
+  printf("sqrt(-1.0) = %f\n", sqrt(-1.0));
+
+  if (errno == EDOM) perror("errno == EDOM");
+
+  if (fetestexcept(FE_INVALID)) puts("FE_INVALID raised");
+
+  return 0;
+}