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[Patch 14/17] [libgcc, ARM] Generalise float-to-half conversion function.

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libgcc/

	* config/arm/fp16.c (struct format): New.
	(binary32): New.
	(__gnu_float2h_internal): New.  Body moved from
	__gnu_f2h_internal and generalize.
	(_gnu_f2h_internal): Move body to function __gnu_float2h_internal.
	Call it with binary32.



Co-Authored-By: Matthew Wahab <matthew.wahab@arm.com>

From-SVN: r242781
This commit is contained in:
James Greenhalgh 2016-11-23 17:30:02 +00:00 committed by James Greenhalgh
parent ba75a1747c
commit 8630cadbc5
2 changed files with 83 additions and 19 deletions
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10
libgcc/ChangeLog
View File

@ -1,3 +1,13 @@
2016-11-23 James Greenhalgh <james.greenhalgh@arm.com>
Matthew Wahab <matthew.wahab@arm.com>
* config/arm/fp16.c (struct format): New.
(binary32): New.
(__gnu_float2h_internal): New. Body moved from
__gnu_f2h_internal and generalize.
(_gnu_f2h_internal): Move body to function __gnu_float2h_internal.
Call it with binary32.
2016-11-23 James Greenhalgh <james.greenhalgh@arm.com>
* soft-fp/extendhftf2.c: Update from glibc.

90
libgcc/config/arm/fp16.c
View File

@ -22,40 +22,74 @@
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
static inline unsigned short
__gnu_f2h_internal(unsigned int a, int ieee)
struct format
{
unsigned short sign = (a >> 16) & 0x8000;
int aexp = (a >> 23) & 0xff;
unsigned int mantissa = a & 0x007fffff;
unsigned int mask;
unsigned int increment;
/* Number of bits. */
unsigned long long size;
/* Exponent bias. */
unsigned long long bias;
/* Exponent width in bits. */
unsigned long long exponent;
/* Significand precision in explicitly stored bits. */
unsigned long long significand;
};
if (aexp == 0xff)
static const struct format
binary32 =
{
32, /* size. */
127, /* bias. */
8, /* exponent. */
23 /* significand. */
};
static inline unsigned short
__gnu_float2h_internal (const struct format* fmt,
unsigned long long a, int ieee)
{
unsigned long long point = 1ULL << fmt->significand;
unsigned short sign = (a >> (fmt->size - 16)) & 0x8000;
int aexp;
unsigned long long mantissa;
unsigned long long mask;
unsigned long long increment;
/* Get the exponent and mantissa encodings. */
mantissa = a & (point - 1);
mask = (1 << fmt->exponent) - 1;
aexp = (a >> fmt->significand) & mask;
/* Infinity, NaN and alternative format special case. */
if (((unsigned int) aexp) == mask)
{
if (!ieee)
return sign;
if (mantissa == 0)
return sign | 0x7c00; /* Infinity. */
/* Remaining cases are NaNs. Convert SNaN to QNaN. */
return sign | 0x7e00 | (mantissa >> 13);
return sign | 0x7e00 | (mantissa >> (fmt->significand - 10));
}
/* Zero. */
if (aexp == 0 && mantissa == 0)
return sign;
aexp -= 127;
/* Construct the exponent and mantissa. */
aexp -= fmt->bias;
/* Decimal point is immediately after the significand. */
mantissa |= point;
/* Decimal point between bits 22 and 23. */
mantissa |= 0x00800000;
if (aexp < -14)
{
mask = 0x00ffffff;
mask = point | (point - 1);
/* Minimum exponent for half-precision is 2^-24. */
if (aexp >= -25)
mask >>= 25 + aexp;
}
else
mask = 0x00001fff;
mask = (point - 1) >> 10;
/* Round. */
if (mantissa & mask)
@ -64,7 +98,7 @@ __gnu_f2h_internal(unsigned int a, int ieee)
if ((mantissa & mask) == increment)
increment = mantissa & (increment << 1);
mantissa += increment;
if (mantissa >= 0x01000000)
if (mantissa >= (point << 1))
{
mantissa >>= 1;
aexp++;
@ -91,9 +125,29 @@ __gnu_f2h_internal(unsigned int a, int ieee)
aexp = -14;
}
/* We leave the leading 1 in the mantissa, and subtract one
from the exponent bias to compensate. */
return sign | (((aexp + 14) << 10) + (mantissa >> 13));
/* Encode the final 16-bit floating-point value.
This is formed of the sign bit, the bias-adjusted exponent, and the
calculated mantissa, with the following caveats:
1. The mantissa calculated after rounding could have a leading 1.
To compensate for this, subtract one from the exponent bias (15)
before adding it to the calculated exponent.
2. When we were calculating rounding, we left the mantissa with the
number of bits of the source operand, it needs reduced to ten
bits (+1 for the afforementioned leading 1) by shifting right by
the number of bits in the source mantissa - 10.
3. To ensure the leading 1 in the mantissa is applied to the exponent
we need to add the mantissa rather than apply an arithmetic "or"
to it. */
return sign | (((aexp + 14) << 10) + (mantissa >> (fmt->significand - 10)));
}
static inline unsigned short
__gnu_f2h_internal (unsigned int a, int ieee)
{
return __gnu_float2h_internal (&binary32, (unsigned long long) a, ieee);
}
unsigned int