From: Richard Henderson <rth@twiddle.net>
To: Petar Jovanovic <Petar.Jovanovic@imgtec.com>
Cc: Petar Jovanovic <petar.jovanovic@rt-rk.com>,
"aurelien@aurel32.net" <aurelien@aurel32.net>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round
Date: Thu, 27 Jun 2013 11:20:33 -0700 [thread overview]
Message-ID: <51CC8271.6040204@twiddle.net> (raw)
In-Reply-To: <56EA75BA695AE044ACFB41322F6D2BF4022320A1@BADAG02.ba.imgtec.org>
On 06/17/2013 03:39 PM, Petar Jovanovic wrote:
> - int64_t temp;
> -
> - temp = (int32_t)a + 0x00008000;
> + uint16_t temp;
>
> - if (a > (int)0x7fff8000) {
> - temp = 0x7FFFFFFF;
> + if (a > 0x7FFF7FFF) {
> + temp = 0x7FFF;
> set_DSPControl_overflow_flag(1, 22, env);
> + } else {
> + temp = ((a + 0x8000) >> 16) & 0xFFFF;
This doesn't look right either, as it doesn't properly check for overflow of
negative values. I'd feel better if we implement this function exactly as
documented, modulo actually using 64-bit arithmetic. How about
int32_t temp;
/* Shift right by one, to avoid needing 64-bit arithmetic. As this A is
signed, this creates the copy of the sign bit as documented. */
a >>= 1;
temp = a + 0x4000;
/* Compare temp{31} with temp{30} by xoring into the sign bit. */
if ((temp ^ (temp << 1)) < 0) {
set_DSPControl_overflow_flag(1, 22, env);
return 0x7fff;
}
return temp >> 15;
r~
next prev parent reply other threads:[~2013-06-27 18:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-22 13:35 [Qemu-devel] [PATCH] target-mips: fix mipsdsp_trunc16_sat16_round Petar Jovanovic
2013-06-09 2:34 ` Petar Jovanovic
2013-06-17 22:39 ` Petar Jovanovic
2013-06-25 10:18 ` Petar Jovanovic
2013-06-27 18:20 ` Richard Henderson [this message]
2013-06-27 21:48 ` Petar Jovanovic
2013-06-28 17:40 ` Richard Henderson
2013-06-30 23:53 ` Petar Jovanovic
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