floatconversion.py
82 lines
| 2.2 KiB
| text/x-python
|
PythonLexer
paul
|
r101 | def ieee(f, word=32): | |
| """Generate the binary string representing a floating-point value in IEEE754 code.""" | |||
| f = float(f) | |||
| if word not in (16, 32, 64, 128): | |||
| raise ValueError("IEEE754 is defined for 16, 32, 64 and 128 bit words.") | |||
| exp_bin = range({16:5, 32:8, 64:11, 128:15}[word]) | |||
| frac_bin = range(word - len(exp_bin) - 1) | |||
| # Sign. | |||
| sign_bin = [int(f < 0)] | |||
| f = abs(f) | |||
| # Find exponent (adding the bias). | |||
| bias = 2**(len(exp_bin)-1) -1 | |||
| exponent = bias | |||
| while f >= 2: | |||
| exponent += 1 | |||
| f /= 2 | |||
| while f < 1 and exponent > 0: | |||
| exponent -= 1 | |||
| f *= 2 | |||
| if not 0 <= exponent < 2*(bias+1): | |||
| raise ValueError("Exponent overflow: Absolute exponent must be smaller than %d." % (bias + 1)) | |||
| # Encode exponent in binary. | |||
| for i in exp_bin[::-1]: | |||
| exp_bin[i] = int(exponent % 2) | |||
| exponent /= 2 | |||
| # Remove the leading 1 bit. | |||
| f -= 1 | |||
| for i in frac_bin: | |||
| f *= 2 | |||
| frac_bin[i] = int(f >= 1) | |||
| f -= frac_bin[i] | |||
| # Join the binary string components together. | |||
| return "".join(map(str, sign_bin + exp_bin + frac_bin)) | |||
| def ieee_decode(binary): | |||
| """Decode a binary string representing a floating-point value in IEEE754 code.""" | |||
| # Determine the word size of the binary. | |||
| word = len(binary) | |||
| if word not in (16, 32, 64, 128): | |||
| raise ValueError("IEEE754 is defined for 16, 32, 64 and 128 bit words.") | |||
| # Determine the length of the exponent. | |||
| e = {16:5, 32:8, 64:11, 128:15}[word] | |||
| # Turn the binary string into a bit-list. | |||
| binary = [int(c) for c in binary] | |||
| # Split the components. | |||
| sign = -2 * binary[0] + 1 | |||
| exp_bin = binary[1:1+e] | |||
| frac_bin = binary[1+e:] | |||
| # Decode the exponent. | |||
| bias = 2**(e-1) - 1 | |||
| exponent = -bias | |||
| c = 1 | |||
| for i in exp_bin[::-1]: | |||
| exponent += i * c | |||
| c *= 2 | |||
| # Decode the fraction. | |||
| f = float(2**exponent) | |||
| power = f | |||
| for i in frac_bin: | |||
| power *= 0.5 | |||
| f += i * power | |||
| return sign * f | |||
| if __name__ == "__main__": | |||
| val = ieee(24.) | |||
| val | |||
| print val[:16] | |||
| print val[0], val[1], val[2] | |||
| val_in_int = int(val[:16], 2) | |||
| print val_in_int | |||
| print hex( val_in_int ) |