alexhudson
ba63bbc4ee
* make it work with automake 1.8 * simpler system for expanding path variables * make it work with older gm4 Thanks to Albert Lee <trisk@acm.jhu.edu> for these!
101 lines
2.6 KiB
Plaintext
101 lines
2.6 KiB
Plaintext
dnl dps_float_byte
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AC_DEFUN([dps_float_byte],
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[AC_MSG_CHECKING(whether ${CXX} supports our byte<->float conversions)
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AC_CACHE_VAL(mdl_cv_have_float_byte_support,
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[ AC_TRY_RUN(
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changequote(<:<, >:>)dnl
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<:<
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typedef long double float_t;
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typedef long int32_t;
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typedef char uint8_t;
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//float to bits conversion utilities...
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union clvalue {
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int32_t i;
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float f; //must use a float type, else types dont match up
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};
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int32_t floatToIntBits(float_t value)
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{
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clvalue u;
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int32_t e, f;
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u.f = value;
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e = u.i & 0x7f800000;
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f = u.i & 0x007fffff;
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if (e == 0x7f800000 && f != 0)
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u.i = 0x7fc00000;
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return u.i;
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}
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float_t intBitsToFloat(int32_t bits)
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{
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clvalue u;
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u.i = bits;
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return u.f;
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}
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float_t byteToFloat(uint8_t b) {
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if (b == 0) // zero is a special case
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return 0.0f;
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int32_t mantissa = b & 7;
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int32_t exponent = (b >> 3) & 31;
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int32_t bits = ((exponent+(63-15)) << 24) | (mantissa << 21);
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return intBitsToFloat(bits);
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}
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uint8_t floatToByte(float_t f) {
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if (f < 0.0f) // round negatives up to zero
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f = 0.0f;
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if (f == 0.0f) // zero is a special case
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return 0;
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int32_t bits = floatToIntBits(f); // parse float_t into parts
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int32_t mantissa = (bits & 0xffffff) >> 21;
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int32_t exponent = (((bits >> 24) & 0x7f) - 63) + 15;
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if (exponent > 31) { // overflow: use max value
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exponent = 31;
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mantissa = 7;
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}
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if (exponent < 0) { // underflow: use min value
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exponent = 0;
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mantissa = 1;
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}
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return (uint8_t)((exponent << 3) | mantissa); // pack into a uint8_t
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}
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int main(void)
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{
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//well know conversion
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if ( floatToByte(0.5f) != 120 )
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return 1;
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//converting back works?
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if ( floatToByte(byteToFloat(57)) != 57 )
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return 1;
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return 0;
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}
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>:>
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changequote([, ]), dps_float_byte_fail=0, dps_float_byte_fail=1,
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dps_float_byte_fail=2
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)]
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)
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if test $dps_float_byte_fail -eq 0; then
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AC_MSG_RESULT([yes])
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AC_DEFINE([HAVE_FUNCTIONING_FLOAT_BYTE], [], [Does not support new float byte<->float conversions])
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elif test $dps_float_byte_fail -eq 1; then
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AC_MSG_RESULT([no])
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AC_DEFINE([HAVE_NO_FLOAT_BYTE], [], [Does not support new float byte<->float conversions])
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else
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AC_MSG_RESULT([unknown, assuming broken])
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AC_DEFINE([HAVE_NO_FLOAT_BYTE], [], [Does not support new float byte<->float conversions])
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fi
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])
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