1 files changed, 152 insertions, 0 deletions

diff --git a/arch/mips/math-emu/dp_sqrt.c b/arch/mips/math-emu/dp_sqrt.c
new file mode 100644
index 000000000..1ee38f824
--- /dev/null
+++ b/arch/mips/math-emu/dp_sqrt.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* IEEE754 floating point arithmetic
+ * double precision square root
+ */
+/*
+ * MIPS floating point support
+ * Copyright (C) 1994-2000 Algorithmics Ltd.
+ */
+
+#include "ieee754dp.h"
+
+static const unsigned int table[] = {
+        0, 1204, 3062, 5746, 9193, 13348, 18162, 23592,
+        29598, 36145, 43202, 50740, 58733, 67158, 75992,
+        85215, 83599, 71378, 60428, 50647, 41945, 34246,
+        27478, 21581, 16499, 12183, 8588, 5674, 3403,
+        1742, 661, 130
+};
+
+union ieee754dp ieee754dp_sqrt(union ieee754dp x)
+{
+        struct _ieee754_csr oldcsr;
+        union ieee754dp y, z, t;
+        unsigned int scalx, yh;
+        COMPXDP;
+
+        EXPLODEXDP;
+        ieee754_clearcx();
+        FLUSHXDP;
+
+        /* x == INF or NAN? */
+        switch (xc) {
+        case IEEE754_CLASS_SNAN:
+                return ieee754dp_nanxcpt(x);
+
+        case IEEE754_CLASS_QNAN:
+                /* sqrt(Nan) = Nan */
+                return x;
+
+        case IEEE754_CLASS_ZERO:
+                /* sqrt(0) = 0 */
+                return x;
+
+        case IEEE754_CLASS_INF:
+                if (xs) {
+                        /* sqrt(-Inf) = Nan */
+                        ieee754_setcx(IEEE754_INVALID_OPERATION);
+                        return ieee754dp_indef();
+                }
+                /* sqrt(+Inf) = Inf */
+                return x;
+
+        case IEEE754_CLASS_DNORM:
+                DPDNORMX;
+                fallthrough;
+        case IEEE754_CLASS_NORM:
+                if (xs) {
+                        /* sqrt(-x) = Nan */
+                        ieee754_setcx(IEEE754_INVALID_OPERATION);
+                        return ieee754dp_indef();
+                }
+                break;
+        }
+
+        /* save old csr; switch off INX enable & flag; set RN rounding */
+        oldcsr = ieee754_csr;
+        ieee754_csr.mx &= ~IEEE754_INEXACT;
+        ieee754_csr.sx &= ~IEEE754_INEXACT;
+        ieee754_csr.rm = FPU_CSR_RN;
+
+        /* adjust exponent to prevent overflow */
+        scalx = 0;
+        if (xe > 512) {         /* x > 2**-512? */
+                xe -= 512;      /* x = x / 2**512 */
+                scalx += 256;
+        } else if (xe < -512) { /* x < 2**-512? */
+                xe += 512;      /* x = x * 2**512 */
+                scalx -= 256;
+        }
+
+        x = builddp(0, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
+        y = x;
+
+        /* magic initial approximation to almost 8 sig. bits */
+        yh = y.bits >> 32;
+        yh = (yh >> 1) + 0x1ff80000;
+        yh = yh - table[(yh >> 15) & 31];
+        y.bits = ((u64) yh << 32) | (y.bits & 0xffffffff);
+
+        /* Heron's rule once with correction to improve to ~18 sig. bits */
+        /* t=x/y; y=y+t; py[n0]=py[n0]-0x00100006; py[n1]=0; */
+        t = ieee754dp_div(x, y);
+        y = ieee754dp_add(y, t);
+        y.bits -= 0x0010000600000000LL;
+        y.bits &= 0xffffffff00000000LL;
+
+        /* triple to almost 56 sig. bits: y ~= sqrt(x) to within 1 ulp */
+        /* t=y*y; z=t;  pt[n0]+=0x00100000; t+=z; z=(x-z)*y; */
+        t = ieee754dp_mul(y, y);
+        z = t;
+        t.bexp += 0x001;
+        t = ieee754dp_add(t, z);
+        z = ieee754dp_mul(ieee754dp_sub(x, z), y);
+
+        /* t=z/(t+x) ;  pt[n0]+=0x00100000; y+=t; */
+        t = ieee754dp_div(z, ieee754dp_add(t, x));
+        t.bexp += 0x001;
+        y = ieee754dp_add(y, t);
+
+        /* twiddle last bit to force y correctly rounded */
+
+        /* set RZ, clear INEX flag */
+        ieee754_csr.rm = FPU_CSR_RZ;
+        ieee754_csr.sx &= ~IEEE754_INEXACT;
+
+        /* t=x/y; ...chopped quotient, possibly inexact */
+        t = ieee754dp_div(x, y);
+
+        if (ieee754_csr.sx & IEEE754_INEXACT || t.bits != y.bits) {
+
+                if (!(ieee754_csr.sx & IEEE754_INEXACT))
+                        /* t = t-ulp */
+                        t.bits -= 1;
+
+                /* add inexact to result status */
+                oldcsr.cx |= IEEE754_INEXACT;
+                oldcsr.sx |= IEEE754_INEXACT;
+
+                switch (oldcsr.rm) {
+                case FPU_CSR_RU:
+                        y.bits += 1;
+                        fallthrough;
+                case FPU_CSR_RN:
+                        t.bits += 1;
+                        break;
+                }
+
+                /* y=y+t; ...chopped sum */
+                y = ieee754dp_add(y, t);
+
+                /* adjust scalx for correctly rounded sqrt(x) */
+                scalx -= 1;
+        }
+
+        /* py[n0]=py[n0]+scalx; ...scale back y */
+        y.bexp += scalx;
+
+        /* restore rounding mode, possibly set inexact */
+        ieee754_csr = oldcsr;
+
+        return y;
+}