[src/trunk]: src/sys/arch/powerpc/fpu Further fix for fcti{w,d}{,z}.

[rin <rin%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/89e042ecf777
branches:  trunk
changeset: 369786:89e042ecf777
user:      rin <rin%NetBSD.org@localhost>
date:      Thu Sep 01 05:56:52 2022 +0000

description:
Further fix for fcti{w,d}{,z}.

- Treat {Q,S}NaN correctly.
- Set exception bits appropriately.
- Introduce round_int().

diffstat:

 sys/arch/powerpc/fpu/fpu_implode.c |  111 ++++++++++++++++++++----------------
 1 files changed, 61 insertions(+), 50 deletions(-)

diffs (183 lines):

diff -r b4fbd12af1e6 -r 89e042ecf777 sys/arch/powerpc/fpu/fpu_implode.c
--- a/sys/arch/powerpc/fpu/fpu_implode.c        Thu Sep 01 05:51:51 2022 +0000
+++ b/sys/arch/powerpc/fpu/fpu_implode.c        Thu Sep 01 05:56:52 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fpu_implode.c,v 1.11 2022/09/01 05:51:51 rin Exp $ */
+/*     $NetBSD: fpu_implode.c,v 1.12 2022/09/01 05:56:52 rin Exp $ */
 
 /*
  * Copyright (c) 1992, 1993
@@ -46,7 +46,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: fpu_implode.c,v 1.11 2022/09/01 05:51:51 rin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: fpu_implode.c,v 1.12 2022/09/01 05:56:52 rin Exp $");
 
 #include <sys/types.h>
 #include <sys/systm.h>
@@ -62,6 +62,7 @@
 
 static int round(struct fpemu *, struct fpn *);
 static int toinf(struct fpemu *, int);
+static int round_int(struct fpn *, int *, int, int, int);
 
 /*
  * Round a number (algorithm from Motorola MC68882 manual, modified for
@@ -189,6 +190,40 @@
        return (inf);
 }
 
+static int
+round_int(struct fpn *fp, int *cx, int rn, int sign, int odd)
+{
+       int g, rs;
+
+       g =   fp->fp_mant[3] & 0x80000000;
+       rs = (fp->fp_mant[3] & 0x7fffffff) | fp->fp_sticky;
+
+       if ((g | rs) == 0)
+               return 0;       /* exact */
+
+       *cx |= FPSCR_XX | FPSCR_FI;
+
+       switch (rn) {
+       case FSR_RD_RN:
+               if (g && (rs | odd))
+                       break;
+               return 0;
+       case FSR_RD_RZ:
+               return 0;
+       case FSR_RD_RP:
+               if (!sign)
+                       break;
+               return 0;
+       case FSR_RD_RM:
+               if (sign)
+                       break;
+               return 0;
+       }
+
+       *cx |= FPSCR_FR;
+       return 1;
+}
+
 /*
  * fpn -> int (int value returned as return value).
  */
@@ -196,10 +231,17 @@
 fpu_ftoi(struct fpemu *fe, struct fpn *fp, int rn)
 {
        u_int i;
-       int sign, exp, g, rs;
+       int sign, exp, cx;
 
        sign = fp->fp_sign;
+       cx = 0;
        switch (fp->fp_class) {
+       case FPC_SNAN:
+               fe->fe_cx |= FPSCR_VXSNAN;
+               /* FALLTHROUGH */
+       case FPC_QNAN:
+               sign = 1;
+               break;
 
        case FPC_ZERO:
                return (0);
@@ -218,34 +260,15 @@
                if ((exp = fp->fp_exp) >= 32)
                        break;
                /* NB: the following includes exp < 0 cases */
-               if (fpu_shr(fp, FP_NMANT - 32 - 1 - exp) != 0)
-                       fe->fe_cx |= FPSCR_UX;
+               (void)fpu_shr(fp, FP_NMANT - 32 - 1 - exp);
                i = fp->fp_mant[2];
-
-               g  =  fp->fp_mant[3] & 0x80000000;
-               rs = (fp->fp_mant[3] & 0x7fffffff) | fp->fp_sticky;
-               switch (rn) {
-               case FSR_RD_RN:
-                       if (g && (rs | (i & 1)))
-                               i++;
-                       break;
-               case FSR_RD_RZ:
-                       break;
-               case FSR_RD_RP:
-                       if (!sign && (g | rs))
-                               i++;
-                       break;
-               case FSR_RD_RM:
-                       if (sign && (g | rs))
-                               i++;
-                       break;
-               }
-
+               i += round_int(fp, &cx, rn, sign, i & 1);
                if (i >= ((u_int)0x80000000 + sign))
                        break;
+               fe->fe_cx |= cx;
                return (sign ? -i : i);
 
-       default:                /* Inf, qNaN, sNaN */
+       case FPC_INF:
                break;
        }
        /* overflow: replace any inexact exception with invalid */
@@ -260,10 +283,17 @@
 fpu_ftox(struct fpemu *fe, struct fpn *fp, int rn)
 {
        uint64_t i;
-       int sign, exp, g, rs;
+       int sign, exp, cx;
 
        sign = fp->fp_sign;
+       cx = 0;
        switch (fp->fp_class) {
+       case FPC_SNAN:
+               fe->fe_cx |= FPSCR_VXSNAN;
+               /* FALLTHROUGH */
+       case FPC_QNAN:
+               sign = 1;
+               break;
 
        case FPC_ZERO:
                return (0);
@@ -282,34 +312,15 @@
                if ((exp = fp->fp_exp) >= 64)
                        break;
                /* NB: the following includes exp < 0 cases */
-               if (fpu_shr(fp, FP_NMANT - 32 - 1 - exp) != 0)
-                       fe->fe_cx |= FPSCR_UX;
+               (void)fpu_shr(fp, FP_NMANT - 32 - 1 - exp);
                i = ((uint64_t)fp->fp_mant[1] << 32) | fp->fp_mant[2];
-
-               g  =  fp->fp_mant[3] & 0x80000000;
-               rs = (fp->fp_mant[3] & 0x7fffffff) | fp->fp_sticky;
-               switch (rn) {
-               case FSR_RD_RN:
-                       if (g && (rs | (i & 1)))
-                               i++;
-                       break;
-               case FSR_RD_RZ:
-                       break;
-               case FSR_RD_RP:
-                       if (!sign && (g | rs))
-                               i++;
-                       break;
-               case FSR_RD_RM:
-                       if (sign && (g | rs))
-                               i++;
-                       break;
-               }
-
+               i += round_int(fp, &cx, rn, sign, i & 1);
                if (i >= ((uint64_t)0x8000000000000000LL + sign))
                        break;
+               fe->fe_cx |= cx;
                return (sign ? -i : i);
 
-       default:                /* Inf, qNaN, sNaN */
+       case FPC_INF:
                break;
        }
        /* overflow: replace any inexact exception with invalid */