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-rw-r--r--fpu/softfloat.c209
1 files changed, 125 insertions, 84 deletions
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 4abcd36b15..c63e011ae8 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -3086,6 +3086,127 @@ static float16 packFloat16(flag zSign, int_fast16_t zExp, uint16_t zSig)
(((uint32_t)zSign) << 15) + (((uint32_t)zExp) << 10) + zSig);
}
+/*----------------------------------------------------------------------------
+| Takes an abstract floating-point value having sign `zSign', exponent `zExp',
+| and significand `zSig', and returns the proper half-precision floating-
+| point value corresponding to the abstract input. Ordinarily, the abstract
+| value is simply rounded and packed into the half-precision format, with
+| the inexact exception raised if the abstract input cannot be represented
+| exactly. However, if the abstract value is too large, the overflow and
+| inexact exceptions are raised and an infinity or maximal finite value is
+| returned. If the abstract value is too small, the input value is rounded to
+| a subnormal number, and the underflow and inexact exceptions are raised if
+| the abstract input cannot be represented exactly as a subnormal half-
+| precision floating-point number.
+| The `ieee' flag indicates whether to use IEEE standard half precision, or
+| ARM-style "alternative representation", which omits the NaN and Inf
+| encodings in order to raise the maximum representable exponent by one.
+| The input significand `zSig' has its binary point between bits 22
+| and 23, which is 13 bits to the left of the usual location. This shifted
+| significand must be normalized or smaller. If `zSig' is not normalized,
+| `zExp' must be 0; in that case, the result returned is a subnormal number,
+| and it must not require rounding. In the usual case that `zSig' is
+| normalized, `zExp' must be 1 less than the ``true'' floating-point exponent.
+| Note the slightly odd position of the binary point in zSig compared with the
+| other roundAndPackFloat functions. This should probably be fixed if we
+| need to implement more float16 routines than just conversion.
+| The handling of underflow and overflow follows the IEC/IEEE Standard for
+| Binary Floating-Point Arithmetic.
+*----------------------------------------------------------------------------*/
+
+static float32 roundAndPackFloat16(flag zSign, int_fast16_t zExp,
+ uint32_t zSig, flag ieee STATUS_PARAM)
+{
+ int maxexp = ieee ? 29 : 30;
+ uint32_t mask;
+ uint32_t increment;
+ int8 roundingMode;
+ bool rounding_bumps_exp;
+ bool is_tiny = false;
+
+ /* Calculate the mask of bits of the mantissa which are not
+ * representable in half-precision and will be lost.
+ */
+ if (zExp < 1) {
+ /* Will be denormal in halfprec */
+ mask = 0x00ffffff;
+ if (zExp >= -11) {
+ mask >>= 11 + zExp;
+ }
+ } else {
+ /* Normal number in halfprec */
+ mask = 0x00001fff;
+ }
+
+ roundingMode = STATUS(float_rounding_mode);
+ switch (roundingMode) {
+ case float_round_nearest_even:
+ increment = (mask + 1) >> 1;
+ if ((zSig & mask) == increment) {
+ increment = zSig & (increment << 1);
+ }
+ break;
+ case float_round_up:
+ increment = zSign ? 0 : mask;
+ break;
+ case float_round_down:
+ increment = zSign ? mask : 0;
+ break;
+ default: /* round_to_zero */
+ increment = 0;
+ break;
+ }
+
+ rounding_bumps_exp = (zSig + increment >= 0x01000000);
+
+ if (zExp > maxexp || (zExp == maxexp && rounding_bumps_exp)) {
+ if (ieee) {
+ float_raise(float_flag_overflow | float_flag_inexact STATUS_VAR);
+ return packFloat16(zSign, 0x1f, 0);
+ } else {
+ float_raise(float_flag_invalid STATUS_VAR);
+ return packFloat16(zSign, 0x1f, 0x3ff);
+ }
+ }
+
+ if (zExp < 0) {
+ /* Note that flush-to-zero does not affect half-precision results */
+ is_tiny =
+ (STATUS(float_detect_tininess) == float_tininess_before_rounding)
+ || (zExp < -1)
+ || (!rounding_bumps_exp);
+ }
+ if (zSig & mask) {
+ float_raise(float_flag_inexact STATUS_VAR);
+ if (is_tiny) {
+ float_raise(float_flag_underflow STATUS_VAR);
+ }
+ }
+
+ zSig += increment;
+ if (rounding_bumps_exp) {
+ zSig >>= 1;
+ zExp++;
+ }
+
+ if (zExp < -10) {
+ return packFloat16(zSign, 0, 0);
+ }
+ if (zExp < 0) {
+ zSig >>= -zExp;
+ zExp = 0;
+ }
+ return packFloat16(zSign, zExp, zSig >> 13);
+}
+
+static void normalizeFloat16Subnormal(uint32_t aSig, int_fast16_t *zExpPtr,
+ uint32_t *zSigPtr)
+{
+ int8_t shiftCount = countLeadingZeros32(aSig) - 21;
+ *zSigPtr = aSig << shiftCount;
+ *zExpPtr = 1 - shiftCount;
+}
+
/* Half precision floats come in two formats: standard IEEE and "ARM" format.
The latter gains extra exponent range by omitting the NaN/Inf encodings. */
@@ -3106,15 +3227,12 @@ float32 float16_to_float32(float16 a, flag ieee STATUS_PARAM)
return packFloat32(aSign, 0xff, 0);
}
if (aExp == 0) {
- int8 shiftCount;
-
if (aSig == 0) {
return packFloat32(aSign, 0, 0);
}
- shiftCount = countLeadingZeros32( aSig ) - 21;
- aSig = aSig << shiftCount;
- aExp = -shiftCount;
+ normalizeFloat16Subnormal(aSig, &aExp, &aSig);
+ aExp--;
}
return packFloat32( aSign, aExp + 0x70, aSig << 13);
}
@@ -3124,12 +3242,6 @@ float16 float32_to_float16(float32 a, flag ieee STATUS_PARAM)
flag aSign;
int_fast16_t aExp;
uint32_t aSig;
- uint32_t mask;
- uint32_t increment;
- int8 roundingMode;
- int maxexp = ieee ? 15 : 16;
- bool rounding_bumps_exp;
- bool is_tiny = false;
a = float32_squash_input_denormal(a STATUS_VAR);
@@ -3164,80 +3276,9 @@ float16 float32_to_float16(float32 a, flag ieee STATUS_PARAM)
* codepath.
*/
aSig |= 0x00800000;
- aExp -= 0x7f;
- /* Calculate the mask of bits of the mantissa which are not
- * representable in half-precision and will be lost.
- */
- if (aExp < -14) {
- /* Will be denormal in halfprec */
- mask = 0x00ffffff;
- if (aExp >= -24) {
- mask >>= 25 + aExp;
- }
- } else {
- /* Normal number in halfprec */
- mask = 0x00001fff;
- }
+ aExp -= 0x71;
- roundingMode = STATUS(float_rounding_mode);
- switch (roundingMode) {
- case float_round_nearest_even:
- increment = (mask + 1) >> 1;
- if ((aSig & mask) == increment) {
- increment = aSig & (increment << 1);
- }
- break;
- case float_round_up:
- increment = aSign ? 0 : mask;
- break;
- case float_round_down:
- increment = aSign ? mask : 0;
- break;
- default: /* round_to_zero */
- increment = 0;
- break;
- }
-
- rounding_bumps_exp = (aSig + increment >= 0x01000000);
-
- if (aExp > maxexp || (aExp == maxexp && rounding_bumps_exp)) {
- if (ieee) {
- float_raise(float_flag_overflow | float_flag_inexact STATUS_VAR);
- return packFloat16(aSign, 0x1f, 0);
- } else {
- float_raise(float_flag_invalid STATUS_VAR);
- return packFloat16(aSign, 0x1f, 0x3ff);
- }
- }
-
- if (aExp < -14) {
- /* Note that flush-to-zero does not affect half-precision results */
- is_tiny =
- (STATUS(float_detect_tininess) == float_tininess_before_rounding)
- || (aExp < -15)
- || (!rounding_bumps_exp);
- }
- if (aSig & mask) {
- float_raise(float_flag_inexact STATUS_VAR);
- if (is_tiny) {
- float_raise(float_flag_underflow STATUS_VAR);
- }
- }
-
- aSig += increment;
- if (rounding_bumps_exp) {
- aSig >>= 1;
- aExp++;
- }
-
- if (aExp < -24) {
- return packFloat16(aSign, 0, 0);
- }
- if (aExp < -14) {
- aSig >>= -14 - aExp;
- aExp = -14;
- }
- return packFloat16(aSign, aExp + 14, aSig >> 13);
+ return roundAndPackFloat16(aSign, aExp, aSig, ieee STATUS_VAR);
}
/*----------------------------------------------------------------------------
generated by cgit v1.2.3 (git 2.26.2) at 2024-12-05 03:18:26 +0000