From 55fb9e2eb179e36dd32a4d05d6d43bdec673e574 Mon Sep 17 00:00:00 2001
From: Rafal Kupiec <belliash@codingworkshop.eu.org>
Date: Wed, 14 Feb 2024 00:02:04 +0100
Subject: [PATCH] Implement RtlGetBaseExponent() routine for getting base(10)
 exponent of a given floating point value

---
 sdk/xtdk/rtltypes.h      |  5 +++
 sdk/xtdk/xttypes.h       | 12 ++++++
 xtoskrnl/CMakeLists.txt  |  1 +
 xtoskrnl/includes/rtli.h |  5 +++
 xtoskrnl/rtl/globals.c   | 13 ++++++
 xtoskrnl/rtl/math.c      | 90 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 126 insertions(+)
 create mode 100644 xtoskrnl/rtl/globals.c

diff --git a/sdk/xtdk/rtltypes.h b/sdk/xtdk/rtltypes.h
index d3fe726..a7a23ec 100644
--- a/sdk/xtdk/rtltypes.h
+++ b/sdk/xtdk/rtltypes.h
@@ -17,6 +17,11 @@
 #define GUID_STRING_LENGTH              38
 #define PARTUUID_STRING_LENGTH          13
 
+/* Floating point definitions */
+#define DOUBLE_EXPONENT_MASK            0x7FF0000000000000ULL
+#define DOUBLE_EXPONENT_SHIFT           0x34
+#define DOUBLE_EXPONENT_BIAS            0x3FF
+
 /* Runtime Library routine callbacks */
 typedef VOID (*PWRITE_CHARACTER)(IN CHAR Character);
 typedef VOID (*PWRITE_WIDE_CHARACTER)(IN WCHAR Character);
diff --git a/sdk/xtdk/xttypes.h b/sdk/xtdk/xttypes.h
index 9388b71..7bf5071 100644
--- a/sdk/xtdk/xttypes.h
+++ b/sdk/xtdk/xttypes.h
@@ -163,6 +163,18 @@ typedef struct _FLOAT128
     LONGLONG HighPart;
 } FLOAT128, *PFLOAT128;
 
+/* 64-bit floating point union */
+typedef union _LARGE_DOUBLE
+{
+    struct
+    {
+        ULONG LowPart;
+        ULONG HighPart;
+    } u;
+    DOUBLE DoublePart;
+    ULONGLONG QuadPart;
+} LARGE_DOUBLE, *PLARGE_DOUBLE;
+
 /* 64-bit signed integer union */
 typedef union _LARGE_INTEGER
 {
diff --git a/xtoskrnl/CMakeLists.txt b/xtoskrnl/CMakeLists.txt
index 0fcc90a..8dc9b81 100644
--- a/xtoskrnl/CMakeLists.txt
+++ b/xtoskrnl/CMakeLists.txt
@@ -41,6 +41,7 @@ list(APPEND XTOSKRNL_SOURCE
     ${XTOSKRNL_SOURCE_DIR}/po/idle.c
     ${XTOSKRNL_SOURCE_DIR}/rtl/atomic.c
     ${XTOSKRNL_SOURCE_DIR}/rtl/byteswap.c
+    ${XTOSKRNL_SOURCE_DIR}/rtl/globals.c
     ${XTOSKRNL_SOURCE_DIR}/rtl/guid.c
     ${XTOSKRNL_SOURCE_DIR}/rtl/ioreg.c
     ${XTOSKRNL_SOURCE_DIR}/rtl/math.c
diff --git a/xtoskrnl/includes/rtli.h b/xtoskrnl/includes/rtli.h
index 57f3b57..5408e37 100644
--- a/xtoskrnl/includes/rtli.h
+++ b/xtoskrnl/includes/rtli.h
@@ -255,6 +255,11 @@ RtlDivideUnsigned64(IN ULONGLONG Dividend,
                     IN ULONGLONG Divisor,
                     OUT PULONGLONG Remainder);
 
+XTAPI
+LONG
+RtlGetBaseExponent(IN DOUBLE Value,
+                   OUT PDOUBLE PowerOfTen);
+
 XTCDECL
 VOID
 RtlInitializeListHead(IN PLIST_ENTRY ListHead);
diff --git a/xtoskrnl/rtl/globals.c b/xtoskrnl/rtl/globals.c
new file mode 100644
index 0000000..c452dd5
--- /dev/null
+++ b/xtoskrnl/rtl/globals.c
@@ -0,0 +1,13 @@
+/**
+ * PROJECT:         ExectOS
+ * COPYRIGHT:       See COPYING.md in the top level directory
+ * FILE:            xtoskrnl/rtl/globals.c
+ * DESCRIPTION:     Kernel runtime library global variables
+ * DEVELOPERS:      Rafal Kupiec <belliash@codingworkshop.eu.org>
+ */
+
+#include <xtos.h>
+
+
+/* This is required for floating numbers to keep LLVM happy */
+int _fltused = 0xFEEDBULL;
diff --git a/xtoskrnl/rtl/math.c b/xtoskrnl/rtl/math.c
index 94e6648..37944d0 100644
--- a/xtoskrnl/rtl/math.c
+++ b/xtoskrnl/rtl/math.c
@@ -510,6 +510,96 @@ RtlDivideLargeInteger(IN LARGE_INTEGER Dividend,
     return LargeInt;
 }
 
+/**
+ * Gets the base exponent of a given floating point value.
+ *
+ * @param Value
+ *        Supplies the floating point value to get the base exponent of.
+ *
+ * @param PowerOfTen
+ *        Supplies a pointer that receives the power of ten associated with the base exponent.
+ *
+ * @return This routine returns the base exponent value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+LONG
+RtlGetBaseExponent(IN DOUBLE Value,
+                   OUT PDOUBLE PowerOfTen)
+{
+    LONG BaseExponent, CurrentExponent, Exponent;
+    ULONG ExponentShift, ExponentMask;
+    LARGE_DOUBLE Parts;
+    DOUBLE Power;
+
+    /* Calculate the exponent mask and shift */
+    ExponentMask = DOUBLE_EXPONENT_MASK >> (sizeof(ULONG) * BITS_PER_BYTE);
+    ExponentShift = DOUBLE_EXPONENT_SHIFT - (sizeof(ULONG) * BITS_PER_BYTE);
+
+    /* Check if value is zero */
+    if(Value == 0.0)
+    {
+        /* Return the power of ten and the exponent */
+        *PowerOfTen = 1.0;
+        return 0;
+    }
+
+    /* Get the parts of the value and calculate the exponent by multiplying by log10(2) */
+    Parts.DoublePart = Value;
+    BaseExponent = ((Parts.u.HighPart & ExponentMask) >> ExponentShift) - DOUBLE_EXPONENT_BIAS;
+    Exponent = (LONG)((DOUBLE)BaseExponent * 0.30102999566) + 1;
+
+    /* Set the initial values and calculate the exponent */
+    CurrentExponent = 0;
+    Power = 1.0;
+    if(Exponent > 0)
+    {
+        /* Calculate the exponent */
+        while(CurrentExponent + 10 <= Exponent)
+        {
+            Power *= 0.0000000001;
+            CurrentExponent += 10;
+        }
+
+        while(CurrentExponent + 1 <= Exponent)
+        {
+            Power *= 0.1;
+            CurrentExponent += 1;
+        }
+    }
+    else
+    {
+        /* Calculate the exponent */
+        while(CurrentExponent - 10 >= Exponent)
+        {
+            Power *= 10000000000;
+            CurrentExponent -= 10;
+        }
+
+        while(CurrentExponent - 1 >= Exponent)
+        {
+            Power *= 10.0;
+            CurrentExponent -= 1;
+        }
+    }
+
+    /* Normalize input value */
+    Value *= Power;
+
+    /* Remove all leading zeros, if any */
+    while((Value != 0.0) && ((LONG)Value == 0))
+    {
+        Value *= 10.0;
+        Exponent -= 1;
+        Power *= 10.0;
+    }
+
+    /* Return the power of ten and the exponent */
+    *PowerOfTen = Power;
+    return Exponent;
+}
+
 /**
  * Multiplies a signed large integer by a signed integer.
  *