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 fuzz-build

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float_format_ints.py

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# Test that integers format to exact values.

for b in [13, 123, 457, 23456]:

for r in range(1, 10):

e_fmt = "{:." + str(r) + "e}"

f_fmt = "{:." + str(r) + "f}"

g_fmt = "{:." + str(r) + "g}"

for e in range(0, 5):

f = b * (10**e)

title = str(b) + " x 10^" + str(e)

print(title, "with format", e_fmt, "gives", e_fmt.format(f))

print(title, "with format", f_fmt, "gives", f_fmt.format(f))

print(title, "with format", g_fmt, "gives", g_fmt.format(f))

# The tests below check border cases involving all mantissa bits.

# In case of REPR_C, where the mantissa is missing two bits, the

# the string representation for such numbers might not always be exactly

# the same but nevertheless be correct, so we must allow a few exceptions.

is_REPR_C = float("1.0000001") == float("1.0")

# 16777215 is 2^24 - 1, the largest integer that can be completely held

# in a float32.

val_str = "{:f}".format(16777215)

# When using REPR_C, 16777215.0 is the same as 16777212.0 or 16777214.4

# (depending on the implementation of pow() function, the result may differ)

if is_REPR_C and (val_str == "16777212.000000" or val_str == "16777214.400000"):

val_str = "16777215.000000"

print(val_str)

# 4294967040 = 16777215 * 128 is the largest integer that is exactly

# represented by a float32 and that will also fit within a (signed) int32.

# The upper bound of our integer-handling code is actually double this,

# but that constant might cause trouble on systems using 32 bit ints.

val_str = "{:f}".format(2147483520)

# When using FLOAT_IMPL_FLOAT, 2147483520.0 == 2147483500.0

# Both representations are valid, the second being "simpler"

is_float32 = float("1e300") == float("inf")

if is_float32 and val_str == "2147483500.000000":

val_str = "2147483520.000000"

# When using REPR_C, 2147483520.0 is the same as 2147483200.0

# Both representations are valid, the second being "simpler"

if is_REPR_C and val_str == "2147483200.000000":

val_str = "2147483520.000000"

print(val_str)

# Very large positive integers can be a test for precision and resolution.

# This is a weird way to represent 1e38 (largest power of 10 for float32).

print("{:.6e}".format(float("9" * 30 + "e8")))