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68 lines
1.6 KiB
68 lines
1.6 KiB
#!/usr/bin/env python2
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#
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# Print out a few IEEE double representations related to the Duktape fastint
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# number model.
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#
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import struct
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import math
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def isFastint(x):
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if math.floor(x) == x and \
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x >= -(2**47) and \
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x < (2**47) and \
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(x != 0 or math.copysign(1.0, x) == 1.0): # Negative zero is a bit tricky
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return True
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return False
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def stringRep(x):
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tmp = struct.pack('>d', x)
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tmphex = tmp.encode('hex')
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sgnexp = (ord(tmp[0]) << 8) + ord(tmp[1])
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sgn = (sgnexp) >> 15
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exp = (sgnexp & 0x7ff0) >> 4
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manthex = tmphex[3:]
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return '%s sgn=%d exp=%d sgnexp=%x manthex=%s' % (tmphex, sgn, exp, sgnexp, manthex)
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def main():
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for i in [ -(2**47) - 1,
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-(2**47),
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-(2**47) + 1,
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-(2**32) - 1,
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-(2**32),
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-(2**32) + 1,
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-(long(0xdeadbeef)),
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-9,
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-8,
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-8,
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-7,
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-6,
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-5,
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-4,
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-3,
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-2,
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-1,
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-0.0, # must use float to get neg zero
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0,
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1,
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2,
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3,
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4,
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5,
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6,
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7,
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8,
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9,
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long(0xdeadbeef),
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(2**32) - 1,
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(2**32),
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(2**32) + 1,
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(2**47) - 1,
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(2**47)
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]:
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print('%f %x (fastint=%s): %s' % (float(i), int(i), str(isFastint(i)), stringRep(i)))
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if __name__ == '__main__':
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main()
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