Rewrite explanatory comments

Author: mrakh

lib/std/rand.zig

@@ -255,6 +255,9 @@ pub const Random = struct {
         // represent every possible value in the available range.
         switch (T) {
             f32 => {
+                // Use 23 random bits for the mantissa, and the rest for the exponent.
+                // If all 41 bits are zero, generate additional random bits, until a
+                // set bit is found, or 126 bits have been generated.
                 const rand = r.int(u64);
                 var rand_lz = @clz(u64, rand | 0x7FFFFF);
                 if (rand_lz == 41) {
@@ -269,6 +272,9 @@ pub const Random = struct {
                 return @bitCast(f32, exponent | mantissa);
             },
             f64 => {
+                // Use 52 random bits for the mantissa, and the rest for the exponent.
+                // If all 12 bits are zero, generate additional random bits, until a
+                // set bit is found, or 1022 bits have been generated.
                 const rand = r.int(u64);
                 var rand_lz: u64 = @clz(u64, rand | 0xFFFFFFFFFFFFF);
                 if (rand_lz == 12) {