__extenddftf2

src/soft_float/float_from_float/__extenddftf2.c

@@ -0,0 +1,96 @@
+/* SPDX-FileCopyrightText: © 2023 Decompollaborate */
+/* SPDX-License-Identifier: MIT */
+
+#include "gcc_vr4300/types.h"
+#include "gcc_vr4300/export.h"
+
+#if ABI_N32 || ABI_N64
+EXPORT(__extenddftf2);
+
+/**
+ * Gets float128 from float64.
+ *
+ * https://gcc.gnu.org/onlinedocs/gccint/the-gcc-low-level-runtime-library/routines-for-floating-point-emulation.html#c.__extenddftf2
+ */
+float128 __extenddftf2(float64 a) {
+    // IEEE754 128-bit floats are encoded in 128 bits as follows:
+    // Sign bit: 1 bit (bit 127)
+    // Encoded exponent: 15 bits (bits 112 ~ 126)
+    // Fraction/Mantissa: 112 bits (bits 0 ~ 111)
+
+    Float128Union ret;
+    Float64Union arg;
+
+    int32_t sign;
+    int32_t encodedExponent;
+    int32_t realExponent;
+    bool mantissaIsZero;
+
+    arg.d = a;
+
+    ret.hex.upper = 0;
+    ret.hex.lower = 0;
+
+    sign = arg.ull >> 63;
+
+    // If parameter is zero, then return zero
+    if ((arg.ull & ~(1ULL << 63)) == 0) {
+        // Preserve the sign
+        ret.hex.upper |= arg.ull & (1ULL << 63);
+        return ret.ld;
+    }
+
+    // Clear up the sign
+    arg.ull &= ~(1ULL << 63);
+
+    encodedExponent = arg.ull >> 52;
+    // Clear up the encoded exponent
+    arg.ull &= ~0x7FF0000000000000ULL;
+
+    // Exponent bias: 0x3FF
+    realExponent = encodedExponent - 0x3FF;
+
+    mantissaIsZero = (arg.ull == 0);
+
+    if (encodedExponent == 0) {
+        // subnormals
+
+        ret.hex.upper |= ((uint64_t)sign) << 63;
+        // no need to set the exponent part since it was already zero'd
+
+        // Set the mantissa
+        ret.hex.upper |= arg.ull >> (52 - 48);
+        ret.hex.lower |= arg.ull << (64 - (52 - 48));
+
+        return ret.ld;
+    }
+
+    if (encodedExponent == 0x7FF) {
+        // Infinity and NaN
+
+        ret.hex.upper |= ((uint64_t)sign) << 63;
+        ret.hex.upper |= 0x7FFF000000000000ULL;
+
+        if (!mantissaIsZero) {
+            // NaN
+
+            // Set the mantissa to any non-zero value
+            ret.hex.lower |= 0xA1F << 16;
+            ret.hex.lower |= 0x4300;
+        }
+
+        return ret.ld;
+    }
+
+    ret.hex.upper |= ((uint64_t)sign) << 63;
+
+    // re-encode the exponent
+    ret.hex.upper |= ((uint64_t)(realExponent + 0x3FFF)) << 48;
+
+    // Set the mantissa
+    ret.hex.upper |= arg.ull >> (52 - 48);
+    ret.hex.lower |= arg.ull << (64 - (52 - 48));
+
+    return ret.ld;
+}
+#endif