Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
---
target/hexagon/arch.h | 35 ++++++
target/hexagon/arch.c | 294 ++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 329 insertions(+)
create mode 100644 target/hexagon/arch.h
create mode 100644 target/hexagon/arch.c
diff --git a/target/hexagon/arch.h b/target/hexagon/arch.h
new file mode 100644
index 0000000..a8374a3
--- /dev/null
+++ b/target/hexagon/arch.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright(c) 2019-2021 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef HEXAGON_ARCH_H
+#define HEXAGON_ARCH_H
+
+#include "qemu/osdep.h"
+#include "qemu/int128.h"
+
+extern uint64_t interleave(uint32_t odd, uint32_t even);
+extern uint64_t deinterleave(uint64_t src);
+extern uint32_t carry_from_add64(uint64_t a, uint64_t b, uint32_t c);
+extern int32_t conv_round(int32_t a, int n);
+extern void arch_fpop_start(CPUHexagonState *env);
+extern void arch_fpop_end(CPUHexagonState *env);
+extern int arch_sf_recip_common(float32 *Rs, float32 *Rt, float32 *Rd,
+ int *adjust, float_status *fp_status);
+extern int arch_sf_invsqrt_common(float32 *Rs, float32 *Rd, int *adjust,
+ float_status *fp_status);
+
+#endif
diff --git a/target/hexagon/arch.c b/target/hexagon/arch.c
new file mode 100644
index 0000000..c59cad5
--- /dev/null
+++ b/target/hexagon/arch.c
@@ -0,0 +1,294 @@
+/*
+ * Copyright(c) 2019-2021 Qualcomm Innovation Center, Inc. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+#include "fpu/softfloat.h"
+#include "cpu.h"
+#include "fma_emu.h"
+#include "arch.h"
+#include "macros.h"
+
+#define SF_BIAS 127
+#define SF_MAXEXP 254
+#define SF_MANTBITS 23
+#define float32_nan make_float32(0xffffffff)
+
+#define BITS_MASK_8 0x5555555555555555ULL
+#define PAIR_MASK_8 0x3333333333333333ULL
+#define NYBL_MASK_8 0x0f0f0f0f0f0f0f0fULL
+#define BYTE_MASK_8 0x00ff00ff00ff00ffULL
+#define HALF_MASK_8 0x0000ffff0000ffffULL
+#define WORD_MASK_8 0x00000000ffffffffULL
+
+uint64_t interleave(uint32_t odd, uint32_t even)
+{
+ /* Convert to long long */
+ uint64_t myodd = odd;
+ uint64_t myeven = even;
+ /* First, spread bits out */
+ myodd = (myodd | (myodd << 16)) & HALF_MASK_8;
+ myeven = (myeven | (myeven << 16)) & HALF_MASK_8;
+ myodd = (myodd | (myodd << 8)) & BYTE_MASK_8;
+ myeven = (myeven | (myeven << 8)) & BYTE_MASK_8;
+ myodd = (myodd | (myodd << 4)) & NYBL_MASK_8;
+ myeven = (myeven | (myeven << 4)) & NYBL_MASK_8;
+ myodd = (myodd | (myodd << 2)) & PAIR_MASK_8;
+ myeven = (myeven | (myeven << 2)) & PAIR_MASK_8;
+ myodd = (myodd | (myodd << 1)) & BITS_MASK_8;
+ myeven = (myeven | (myeven << 1)) & BITS_MASK_8;
+ /* Now OR together */
+ return myeven | (myodd << 1);
+}
+
+uint64_t deinterleave(uint64_t src)
+{
+ /* Get odd and even bits */
+ uint64_t myodd = ((src >> 1) & BITS_MASK_8);
+ uint64_t myeven = (src & BITS_MASK_8);
+
+ /* Unspread bits */
+ myeven = (myeven | (myeven >> 1)) & PAIR_MASK_8;
+ myodd = (myodd | (myodd >> 1)) & PAIR_MASK_8;
+ myeven = (myeven | (myeven >> 2)) & NYBL_MASK_8;
+ myodd = (myodd | (myodd >> 2)) & NYBL_MASK_8;
+ myeven = (myeven | (myeven >> 4)) & BYTE_MASK_8;
+ myodd = (myodd | (myodd >> 4)) & BYTE_MASK_8;
+ myeven = (myeven | (myeven >> 8)) & HALF_MASK_8;
+ myodd = (myodd | (myodd >> 8)) & HALF_MASK_8;
+ myeven = (myeven | (myeven >> 16)) & WORD_MASK_8;
+ myodd = (myodd | (myodd >> 16)) & WORD_MASK_8;
+
+ /* Return odd bits in upper half */
+ return myeven | (myodd << 32);
+}
+
+uint32_t carry_from_add64(uint64_t a, uint64_t b, uint32_t c)
+{
+ uint64_t tmpa, tmpb, tmpc;
+ tmpa = fGETUWORD(0, a);
+ tmpb = fGETUWORD(0, b);
+ tmpc = tmpa + tmpb + c;
+ tmpa = fGETUWORD(1, a);
+ tmpb = fGETUWORD(1, b);
+ tmpc = tmpa + tmpb + fGETUWORD(1, tmpc);
+ tmpc = fGETUWORD(1, tmpc);
+ return tmpc;
+}
+
+int32_t conv_round(int32_t a, int n)
+{
+ int64_t val;
+
+ if (n == 0) {
+ val = a;
+ } else if ((a & ((1 << (n - 1)) - 1)) == 0) { /* N-1..0 all zero? */
+ /* Add LSB from int part */
+ val = ((fSE32_64(a)) + (int64_t) (((uint32_t) ((1 << n) & a)) >> 1));
+ } else {
+ val = ((fSE32_64(a)) + (1 << (n - 1)));
+ }
+
+ val = val >> n;
+ return (int32_t)val;
+}
+
+/* Floating Point Stuff */
+
+static const int softfloat_roundingmodes[] = {
+ float_round_nearest_even,
+ float_round_to_zero,
+ float_round_down,
+ float_round_up,
+};
+
+void arch_fpop_start(CPUHexagonState *env)
+{
+ set_float_exception_flags(0, &env->fp_status);
+ set_float_rounding_mode(
+ softfloat_roundingmodes[fREAD_REG_FIELD(USR, USR_FPRND)],
+ &env->fp_status);
+}
+
+#define RAISE_FP_EXCEPTION \
+ do {} while (0) /* Not modelled in qemu user mode */
+
+#define SOFTFLOAT_TEST_FLAG(FLAG, MYF, MYE) \
+ do { \
+ if (flags & FLAG) { \
+ if (GET_USR_FIELD(USR_##MYF) == 0) { \
+ SET_USR_FIELD(USR_##MYF, 1); \
+ if (GET_USR_FIELD(USR_##MYE)) { \
+ RAISE_FP_EXCEPTION; \
+ } \
+ } \
+ } \
+ } while (0)
+
+void arch_fpop_end(CPUHexagonState *env)
+{
+ int flags = get_float_exception_flags(&env->fp_status);
+ if (flags != 0) {
+ SOFTFLOAT_TEST_FLAG(float_flag_inexact, FPINPF, FPINPE);
+ SOFTFLOAT_TEST_FLAG(float_flag_divbyzero, FPDBZF, FPDBZE);
+ SOFTFLOAT_TEST_FLAG(float_flag_invalid, FPINVF, FPINVE);
+ SOFTFLOAT_TEST_FLAG(float_flag_overflow, FPOVFF, FPOVFE);
+ SOFTFLOAT_TEST_FLAG(float_flag_underflow, FPUNFF, FPUNFE);
+ }
+}
+
+static float32 float32_mul_pow2(float32 a, uint32_t p, float_status *fp_status)
+{
+ float32 b = make_float32((SF_BIAS + p) << SF_MANTBITS);
+ return float32_mul(a, b, fp_status);
+}
+
+int arch_sf_recip_common(float32 *Rs, float32 *Rt, float32 *Rd, int *adjust,
+ float_status *fp_status)
+{
+ int n_exp;
+ int d_exp;
+ int ret = 0;
+ float32 RsV, RtV, RdV;
+ int PeV = 0;
+ RsV = *Rs;
+ RtV = *Rt;
+ if (float32_is_any_nan(RsV) && float32_is_any_nan(RtV)) {
+ if (extract32(RsV & RtV, 22, 1) == 0) {
+ float_raise(float_flag_invalid, fp_status);
+ }
+ RdV = RsV = RtV = float32_nan;
+ } else if (float32_is_any_nan(RsV)) {
+ if (extract32(RsV, 22, 1) == 0) {
+ float_raise(float_flag_invalid, fp_status);
+ }
+ RdV = RsV = RtV = float32_nan;
+ } else if (float32_is_any_nan(RtV)) {
+ /* or put NaN in num/den fixup? */
+ if (extract32(RtV, 22, 1) == 0) {
+ float_raise(float_flag_invalid, fp_status);
+ }
+ RdV = RsV = RtV = float32_nan;
+ } else if (float32_is_infinity(RsV) && float32_is_infinity(RtV)) {
+ /* or put Inf in num fixup? */
+ RdV = RsV = RtV = float32_nan;
+ float_raise(float_flag_invalid, fp_status);
+ } else if (float32_is_zero(RsV) && float32_is_zero(RtV)) {
+ /* or put zero in num fixup? */
+ RdV = RsV = RtV = float32_nan;
+ float_raise(float_flag_invalid, fp_status);
+ } else if (float32_is_zero(RtV)) {
+ /* or put Inf in num fixup? */
+ uint8_t RsV_sign = float32_is_neg(RsV);
+ uint8_t RtV_sign = float32_is_neg(RtV);
+ RsV = infinite_float32(RsV_sign ^ RtV_sign);
+ RtV = float32_one;
+ RdV = float32_one;
+ if (float32_is_infinity(RsV)) {
+ float_raise(float_flag_divbyzero, fp_status);
+ }
+ } else if (float32_is_infinity(RtV)) {
+ RsV = make_float32(0x80000000 & (RsV ^ RtV));
+ RtV = float32_one;
+ RdV = float32_one;
+ } else if (float32_is_zero(RsV)) {
+ /* Does this just work itself out? */
+ /* No, 0/Inf causes problems. */
+ RsV = make_float32(0x80000000 & (RsV ^ RtV));
+ RtV = float32_one;
+ RdV = float32_one;
+ } else if (float32_is_infinity(RsV)) {
+ uint8_t RsV_sign = float32_is_neg(RsV);
+ uint8_t RtV_sign = float32_is_neg(RtV);
+ RsV = infinite_float32(RsV_sign ^ RtV_sign);
+ RtV = float32_one;
+ RdV = float32_one;
+ } else {
+ PeV = 0x00;
+ /* Basic checks passed */
+ n_exp = float32_getexp(RsV);
+ d_exp = float32_getexp(RtV);
+ if ((n_exp - d_exp + SF_BIAS) <= SF_MANTBITS) {
+ /* Near quotient underflow / inexact Q */
+ PeV = 0x80;
+ RtV = float32_mul_pow2(RtV, -64, fp_status);
+ RsV = float32_mul_pow2(RsV, 64, fp_status);
+ } else if ((n_exp - d_exp + SF_BIAS) > (SF_MAXEXP - 24)) {
+ /* Near quotient overflow */
+ PeV = 0x40;
+ RtV = float32_mul_pow2(RtV, 32, fp_status);
+ RsV = float32_mul_pow2(RsV, -32, fp_status);
+ } else if (n_exp <= SF_MANTBITS + 2) {
+ RtV = float32_mul_pow2(RtV, 64, fp_status);
+ RsV = float32_mul_pow2(RsV, 64, fp_status);
+ } else if (d_exp <= 1) {
+ RtV = float32_mul_pow2(RtV, 32, fp_status);
+ RsV = float32_mul_pow2(RsV, 32, fp_status);
+ } else if (d_exp > 252) {
+ RtV = float32_mul_pow2(RtV, -32, fp_status);
+ RsV = float32_mul_pow2(RsV, -32, fp_status);
+ }
+ RdV = 0;
+ ret = 1;
+ }
+ *Rs = RsV;
+ *Rt = RtV;
+ *Rd = RdV;
+ *adjust = PeV;
+ return ret;
+}
+
+int arch_sf_invsqrt_common(float32 *Rs, float32 *Rd, int *adjust,
+ float_status *fp_status)
+{
+ float32 RsV, RdV;
+ int PeV = 0;
+ int r_exp;
+ int ret = 0;
+ RsV = *Rs;
+ if (float32_is_infinity(RsV)) {
+ if (extract32(RsV, 22, 1) == 0) {
+ float_raise(float_flag_invalid, fp_status);
+ }
+ RdV = RsV = float32_nan;
+ } else if (float32_lt(RsV, float32_zero, fp_status)) {
+ /* Negative nonzero values are NaN */
+ float_raise(float_flag_invalid, fp_status);
+ RsV = float32_nan;
+ RdV = float32_nan;
+ } else if (float32_is_infinity(RsV)) {
+ /* or put Inf in num fixup? */
+ RsV = infinite_float32(1);
+ RdV = infinite_float32(1);
+ } else if (float32_is_zero(RsV)) {
+ /* or put zero in num fixup? */
+ RdV = float32_one;
+ } else {
+ PeV = 0x00;
+ /* Basic checks passed */
+ r_exp = float32_getexp(RsV);
+ if (r_exp <= 24) {
+ RsV = float32_mul_pow2(RsV, 64, fp_status);
+ PeV = 0xe0;
+ }
+ RdV = 0;
+ ret = 1;
+ }
+ *Rs = RsV;
+ *Rd = RdV;
+ *adjust = PeV;
+ return ret;
+}
--
2.7.4
Hi Taylor,
On 1/20/21 4:28 AM, Taylor Simpson wrote:
> Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
> ---
> target/hexagon/arch.h | 35 ++++++
> target/hexagon/arch.c | 294 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 329 insertions(+)
> create mode 100644 target/hexagon/arch.h
> create mode 100644 target/hexagon/arch.c
>
> diff --git a/target/hexagon/arch.h b/target/hexagon/arch.h
> new file mode 100644
> index 0000000..a8374a3
> --- /dev/null
> +++ b/target/hexagon/arch.h
Maybe rename "arch_utils.[ch]"?
> @@ -0,0 +1,35 @@
> +/*
> + * Copyright(c) 2019-2021 Qualcomm Innovation Center, Inc. All Rights Reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef HEXAGON_ARCH_H
> +#define HEXAGON_ARCH_H
> +
> +#include "qemu/osdep.h"
> +#include "qemu/int128.h"
> +
> +extern uint64_t interleave(uint32_t odd, uint32_t even);
> +extern uint64_t deinterleave(uint64_t src);
> +extern uint32_t carry_from_add64(uint64_t a, uint64_t b, uint32_t c);
> +extern int32_t conv_round(int32_t a, int n);
> +extern void arch_fpop_start(CPUHexagonState *env);
> +extern void arch_fpop_end(CPUHexagonState *env);
> +extern int arch_sf_recip_common(float32 *Rs, float32 *Rt, float32 *Rd,
> + int *adjust, float_status *fp_status);
> +extern int arch_sf_invsqrt_common(float32 *Rs, float32 *Rd, int *adjust,
> + float_status *fp_status);
(Again, no need for 'extern').
> +
> +#endif
> diff --git a/target/hexagon/arch.c b/target/hexagon/arch.c
> new file mode 100644
> index 0000000..c59cad5
> --- /dev/null
> +++ b/target/hexagon/arch.c
...
> +#define RAISE_FP_EXCEPTION \
> + do {} while (0) /* Not modelled in qemu user mode */
I don't understand why... Can you explain please?
> +
> +#define SOFTFLOAT_TEST_FLAG(FLAG, MYF, MYE) \
> + do { \
> + if (flags & FLAG) { \
> + if (GET_USR_FIELD(USR_##MYF) == 0) { \
> + SET_USR_FIELD(USR_##MYF, 1); \
> + if (GET_USR_FIELD(USR_##MYE)) { \
> + RAISE_FP_EXCEPTION; \
> + } \
> + } \
> + } \
> + } while (0)
...
> -----Original Message-----
> From: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com> On
> Behalf Of Philippe Mathieu-Daudé
> Sent: Friday, January 22, 2021 12:09 PM
> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
> Cc: richard.henderson@linaro.org; alex.bennee@linaro.org;
> laurent@vivier.eu; ale@rev.ng; Brian Cain <bcain@quicinc.com>
> Subject: Re: [PATCH v7 15/35] Hexagon (target/hexagon/arch.[ch]) utility
> functions
>
> Hi Taylor,
>
> On 1/20/21 4:28 AM, Taylor Simpson wrote:
> > Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
> > ---
> > target/hexagon/arch.h | 35 ++++++
> > target/hexagon/arch.c | 294
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 329 insertions(+)
> > create mode 100644 target/hexagon/arch.h
> > create mode 100644 target/hexagon/arch.c
> >
> > diff --git a/target/hexagon/arch.h b/target/hexagon/arch.h
> > new file mode 100644
> > index 0000000..a8374a3
> > --- /dev/null
> > +++ b/target/hexagon/arch.h
>
> Maybe rename "arch_utils.[ch]"?
Any particular reason?
>
> > +extern int arch_sf_invsqrt_common(float32 *Rs, float32 *Rd, int *adjust,
> > + float_status *fp_status);
>
> (Again, no need for 'extern').
OK, I will change these.
> > diff --git a/target/hexagon/arch.c b/target/hexagon/arch.c
> > new file mode 100644
> > index 0000000..c59cad5
> > --- /dev/null
> > +++ b/target/hexagon/arch.c
> ...
>
> > +#define RAISE_FP_EXCEPTION \
> > + do {} while (0) /* Not modelled in qemu user mode */
>
> I don't understand why... Can you explain please?
Our Linux kernel only sets the relevant bits in USR (user status register). The exception isn't raised to user mode.
On 1/22/21 10:59 PM, Taylor Simpson wrote:
>> -----Original Message-----
>> From: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com> On
>> Behalf Of Philippe Mathieu-Daudé
>> Sent: Friday, January 22, 2021 12:09 PM
>> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
>> Cc: richard.henderson@linaro.org; alex.bennee@linaro.org;
>> laurent@vivier.eu; ale@rev.ng; Brian Cain <bcain@quicinc.com>
>> Subject: Re: [PATCH v7 15/35] Hexagon (target/hexagon/arch.[ch]) utility
>> functions
>>
>> Hi Taylor,
>>
>> On 1/20/21 4:28 AM, Taylor Simpson wrote:
>>> Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
>>> ---
>>> target/hexagon/arch.h | 35 ++++++
>>> target/hexagon/arch.c | 294
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 329 insertions(+)
>>> create mode 100644 target/hexagon/arch.h
>>> create mode 100644 target/hexagon/arch.c
>>>
>>> diff --git a/target/hexagon/arch.h b/target/hexagon/arch.h
>>> new file mode 100644
>>> index 0000000..a8374a3
>>> --- /dev/null
>>> +++ b/target/hexagon/arch.h
>>
>> Maybe rename "arch_utils.[ch]"?
>
> Any particular reason?
I was thinking about not being confused by an architecture specific
file when doing refactors involving multiple architectures. But this
isn't a great improvement neither... No problem.
>
>>
>>> +extern int arch_sf_invsqrt_common(float32 *Rs, float32 *Rd, int *adjust,
>>> + float_status *fp_status);
>>
>> (Again, no need for 'extern').
>
> OK, I will change these.
>
>>> diff --git a/target/hexagon/arch.c b/target/hexagon/arch.c
>>> new file mode 100644
>>> index 0000000..c59cad5
>>> --- /dev/null
>>> +++ b/target/hexagon/arch.c
>> ...
>>
>>> +#define RAISE_FP_EXCEPTION \
>>> + do {} while (0) /* Not modelled in qemu user mode */
>>
>> I don't understand why... Can you explain please?
>
> Our Linux kernel only sets the relevant bits in USR (user status register). The exception isn't raised to user mode.
Hmm while you introduce the linux-user implementation of your port,
this file is not restricted to user mode. Thinking about avoiding
head aches to someone wanting to add system mode emulation (or a
BSD port??), maybe your helpers should consider that.
Maybe some cheap #ifdef'ry CONFIG_USER_ONLY with a comment explaining
why there is nothing to do in user mode, and g_assert_not_reached()
else. Not sure, just wondering...
Regards,
Phil.
> -----Original Message-----
> From: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com> On
> Behalf Of Philippe Mathieu-Daudé
> Sent: Monday, January 25, 2021 10:30 AM
> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
> Cc: ale@rev.ng; alex.bennee@linaro.org; richard.henderson@linaro.org;
> laurent@vivier.eu; Brian Cain <bcain@quicinc.com>
> Subject: Re: [PATCH v7 15/35] Hexagon (target/hexagon/arch.[ch]) utility
> functions
>
> >>> diff --git a/target/hexagon/arch.c b/target/hexagon/arch.c
> >>> new file mode 100644
> >>> index 0000000..c59cad5
> >>> --- /dev/null
> >>> +++ b/target/hexagon/arch.c
> >> ...
> >>
> >>> +#define RAISE_FP_EXCEPTION \
> >>> + do {} while (0) /* Not modelled in qemu user mode */
> >>
> >> I don't understand why... Can you explain please?
> >
> > Our Linux kernel only sets the relevant bits in USR (user status register).
> The exception isn't raised to user mode.
>
> Hmm while you introduce the linux-user implementation of your port,
> this file is not restricted to user mode. Thinking about avoiding
> head aches to someone wanting to add system mode emulation (or a
> BSD port??), maybe your helpers should consider that.
> Maybe some cheap #ifdef'ry CONFIG_USER_ONLY with a comment
> explaining
> why there is nothing to do in user mode, and g_assert_not_reached()
> else. Not sure, just wondering...
Sorry, I misunderstood the question. You are correct. It's a placeholder for future work to support system mode. I'll add the #ifdef and some comments to explain.
Thanks,
Taylor
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