Floating-Point

IEEE 754-1985, 754-2008
IEEE single-precision standard (binary32) - 32 bits
IEEE double-precision standard (binary64) - 64 bits

single-recision (binary32) -
1 bit - sign (S)
8 bits - exponention (E)
23 bits - mantissa (M)

Number = (-1)^S×1.M×^E-127

Reference:

Tutorial: Floating-Point Binary
Floating point ALU using VHDL implemented on FPGA
Single-precision floating-point format (Wikipedia)
Double-precision floating-point format (Wikipedia)