On 12/3/19 10:31 AM, Stam Markianos-Wright wrote:
>
>
> On 12/2/19 9:27 PM, Joseph Myers wrote:
>> On Mon, 2 Dec 2019, Jeff Law wrote:
>>
>>>> 2019-11-13 Stam Markianos-Wright <[email protected]>
>>>>
>>>> * real.c (struct arm_bfloat_half_format,
>>>> encode_arm_bfloat_half, decode_arm_bfloat_half): New.
>>>> * real.h (arm_bfloat_half_format): New.
>>>>
>>>>
>>> Generally OK. Please consider using "arm_bfloat_half" instead of
>>> "bfloat_half" for the name field in the arm_bfloat_half_format
>>> structure. I'm not sure if that's really visible externally, but it
>>
> Hi both! Agreed that we want to be conservative. See latest diff
> attached with the name field change (also pasted below).
.Ping :)
>
>> Isn't this the same format used by AVX512_BF16 / Intel DL Boost (albeit
>> with Arm and Intel using different rounding modes)?
>
> Yes it is remarkably similar, but there's really only so much variation
> you can have with what is half an f32!
>
> Cheers,
> Stam
>
>
>>
>
>
> diff --git a/gcc/real.h b/gcc/real.h
> index 0f660c9c671..2b337bb7f7d 100644
> --- a/gcc/real.h
> +++ b/gcc/real.h
> @@ -368,6 +368,7 @@ extern const struct real_format decimal_double_format;
> extern const struct real_format decimal_quad_format;
> extern const struct real_format ieee_half_format;
> extern const struct real_format arm_half_format;
> +extern const struct real_format arm_bfloat_half_format;
>
>
> /*
> ====================================================================== */
> diff --git a/gcc/real.c b/gcc/real.c
> index 134240a6be9..07b63b6f27e 100644
> --- a/gcc/real.c
> +++ b/gcc/real.c
> @@ -4799,6 +4799,116 @@ decode_ieee_half (const struct real_format *fmt,
> REAL_VALUE_TYPE *r,
> }
> }
>
> +/* Encode arm_bfloat types. */
> +static void
> +encode_arm_bfloat_half (const struct real_format *fmt, long *buf,
> + const REAL_VALUE_TYPE *r)
> +{
> + unsigned long image, sig, exp;
> + unsigned long sign = r->sign;
> + bool denormal = (r->sig[SIGSZ-1] & SIG_MSB) == 0;
> +
> + image = sign << 15;
> + sig = (r->sig[SIGSZ-1] >> (HOST_BITS_PER_LONG - 8)) & 0x7f;
> +
> + switch (r->cl)
> + {
> + case rvc_zero:
> + break;
> +
> + case rvc_inf:
> + if (fmt->has_inf)
> + image |= 255 << 7;
> + else
> + image |= 0x7fff;
> + break;
> +
> + case rvc_nan:
> + if (fmt->has_nans)
> + {
> + if (r->canonical)
> + sig = (fmt->canonical_nan_lsbs_set ? (1 << 6) - 1 : 0);
> + if (r->signalling == fmt->qnan_msb_set)
> + sig &= ~(1 << 6);
> + else
> + sig |= 1 << 6;
> + if (sig == 0)
> + sig = 1 << 5;
> +
> + image |= 255 << 7;
> + image |= sig;
> + }
> + else
> + image |= 0x7fff;
> + break;
> +
> + case rvc_normal:
> + if (denormal)
> + exp = 0;
> + else
> + exp = REAL_EXP (r) + 127 - 1;
> + image |= exp << 7;
> + image |= sig;
> + break;
> +
> + default:
> + gcc_unreachable ();
> + }
> +
> + buf[0] = image;
> +}
> +
> +/* Decode arm_bfloat types. */
> +static void
> +decode_arm_bfloat_half (const struct real_format *fmt, REAL_VALUE_TYPE *r,
> + const long *buf)
> +{
> + unsigned long image = buf[0] & 0xffff;
> + bool sign = (image >> 15) & 1;
> + int exp = (image >> 7) & 0xff;
> +
> + memset (r, 0, sizeof (*r));
> + image <<= HOST_BITS_PER_LONG - 8;
> + image &= ~SIG_MSB;
> +
> + if (exp == 0)
> + {
> + if (image && fmt->has_denorm)
> + {
> + r->cl = rvc_normal;
> + r->sign = sign;
> + SET_REAL_EXP (r, -126);
> + r->sig[SIGSZ-1] = image << 1;
> + normalize (r);
> + }
> + else if (fmt->has_signed_zero)
> + r->sign = sign;
> + }
> + else if (exp == 255 && (fmt->has_nans || fmt->has_inf))
> + {
> + if (image)
> + {
> + r->cl = rvc_nan;
> + r->sign = sign;
> + r->signalling = (((image >> (HOST_BITS_PER_LONG - 2)) & 1)
> + ^ fmt->qnan_msb_set);
> + r->sig[SIGSZ-1] = image;
> + }
> + else
> + {
> + r->cl = rvc_inf;
> + r->sign = sign;
> + }
> + }
> + else
> + {
> + r->cl = rvc_normal;
> + r->sign = sign;
> + SET_REAL_EXP (r, exp - 127 + 1);
> + r->sig[SIGSZ-1] = image | SIG_MSB;
> + }
> +}
> +
> /* Half-precision format, as specified in IEEE 754R. */
> const struct real_format ieee_half_format =
> {
> @@ -4848,6 +4958,33 @@ const struct real_format arm_half_format =
> false,
> "arm_half"
> };
> +
> +/* ARM Bfloat half-precision format. This format resembles a truncated
> + (16-bit) version of the 32-bit IEEE 754 single-precision floating-point
> + format. */
> +const struct real_format arm_bfloat_half_format =
> + {
> + encode_arm_bfloat_half,
> + decode_arm_bfloat_half,
> + 2,
> + 8,
> + 8,
> + -125,
> + 128,
> + 15,
> + 15,
> + 0,
> + false,
> + true,
> + true,
> + true,
> + true,
> + true,
> + true,
> + false,
> + "arm_bfloat_half"
> + };
> +
>
> /* A synthetic "format" for internal arithmetic. It's the size of the
> internal significand minus the two bits needed for proper rounding.
