Git conversion: Make reactos the root directory, move rosapps, rostests, wallpapers into modules, and delete rossubsys.

sdk/lib/crt/math/amd64/sqrt.c

@@ -0,0 +1,77 @@
+
+#include <intrin.h>
+
+double
+sqrt (
+    double x)
+{
+    register union
+    {
+        __m128d x128d;
+        __m128i x128i;
+    } u ;
+    register union
+    {
+        unsigned long long ullx;
+        double dbl;
+    } u2;
+
+    /* Set the lower double-precision value of u to x.
+       All that we want, is that the compiler understands that we have the
+       function parameter in a register that we can address as an __m128.
+       Sadly there is no obvious way to do that. If we use the union, VS will
+       generate code to store xmm0 in memory and the read it into a GPR.
+       We avoid memory access by using a direct move. But even here we won't
+       get a simple MOVSD. We can either do:
+       a) _mm_set_sd: move x into the lower part of an xmm register and zero
+          out the upper part (XORPD+MOVSD)
+       b) _mm_set1_pd: move x into the lower and higher part of an xmm register
+         (MOVSD+UNPCKLPD)
+       c) _mm_set_pd, which either generates a memory access, when we try to
+          tell it to keep the upper 64 bits, or generate 2 MOVAPS + UNPCKLPD
+       We choose a, which is probably the fastest.
+    */
+    u.x128d = _mm_set_sd(x);
+
+    /* Move the contents of the lower 64 bit into a 64 bit GPR using MOVD */
+    u2.ullx = _mm_cvtsi128_si64(u.x128i);
+
+    /* Check for negative values */
+    if (u2.ullx & 0x8000000000000000ULL)
+    {
+        /* Check if this is *really* negative and not just -0.0 */
+        if (u2.ullx != 0x8000000000000000ULL)
+        {
+            /* Return -1.#IND00 */
+            u2.ullx = 0xfff8000000000000ULL;
+        }
+
+        /* Return what we have */
+        return u2.dbl;
+    }
+
+    /* Check if this is a NaN (bits 52-62 are 1, bit 0-61 are not all 0) or
+       negative (bit 63 is 1) */
+    if (u2.ullx > 0x7FF0000000000000ULL)
+    {
+        /* Set this bit. That's what MS function does. */
+        u2.ullx |= 0x8000000000000ULL;
+        return u2.dbl;
+    }
+
+    /* Calculate the square root. */
+#ifdef _MSC_VER
+    /* Another YAY for the MS compiler. There are 2 instructions we could use:
+       SQRTPD (computes sqrt for 2 double values) or SQRTSD (computes sqrt for
+       only the lower 64 bit double value). Obviously we only need 1. And on
+       Some architectures SQRTPD is twice as slow as SQRTSD. On the other hand
+       the MS compiler is stupid and always generates an additional MOVAPS
+       instruction when SQRTSD is used. We choose to use SQRTPD here since on
+       modern hardware it's as fast as SQRTSD. */
+    u.x128d = _mm_sqrt_pd(u.x128d); // SQRTPD
+#else
+    u.x128d = _mm_sqrt_sd(u.x128d, u.x128d); // SQRTSD
+#endif
+
+    return u.x128d.m128d_f64[0];
+}