[util] Add util::format replacement for snprintf

The printf library I have been using, while useful, has way more than I
need in it, and had comparably huge stack space requirements. This
change adds a new util::format() which is a replacement for snprintf,
but with only the features used by kernel logging.

The logger has been changed to use it, as well as the few instances of
snprintf in the interrupt handling code before calling kassert.

Also part of this change: the logger's (now vestigial) immediate output
handling code is removed, as well as the "sequence" field on log
message headers.

src/libraries/util/format.cpp

@@ -0,0 +1,133 @@
+#include <stdarg.h>
+#include <util/format.h>
+
+namespace util {
+
+namespace {
+
+const char digits[] = "0123456789abcdef";
+
+template <typename I, unsigned N> void
+append_int(char *&out, size_t &count, size_t max, I value, unsigned min_width, char pad)
+{
+    static constexpr size_t bufsize = sizeof(I)*3;
+
+    unsigned num_digits = 0;
+    char buffer[bufsize];
+    char *p = buffer + (bufsize - 1);
+    do {
+        if (value) {
+            *p-- = digits[value % N];
+            value /= N;
+        } else {
+            *p-- = num_digits ? pad : '0';
+        }
+        num_digits++;
+    } while (value || num_digits < min_width);
+
+    ++p;
+    for (unsigned i = 0; i < num_digits; ++i) {
+        *out++ = p[i];
+        if (++count == max)
+            return;
+    }
+}
+
+void
+append_string(char *&out, size_t &count, size_t max, char const *value)
+{
+    while (value && *value && count < max) {
+        count++;
+        *out++ = *value++;
+    }
+}
+
+} // namespace
+
+size_t
+vformat(stringbuf output, char const *format, va_list va)
+{
+    char * out = output.pointer;
+    const size_t max = output.count - 1;
+
+    size_t count = 0;
+    while (format && *format && count < max) {
+        if (*format != '%') {
+            count++;
+            *out++ = *format++;
+            continue;
+        }
+
+        format++; // chomp the % character
+        char spec = *format++;
+
+        bool long_type = false;
+        if (spec == '%') {
+            count++;
+            *out++ = '%';
+            continue;
+        }
+
+        unsigned width = 0;
+        char pad = ' ';
+
+        while (spec) {
+            bool done = false;
+
+            if (spec >= '0' && spec <= '9') {
+                if (spec == '0' && width == 0)
+                    pad = '0';
+                else
+                    width = width * 10 + (spec - '0');
+
+                spec = *format++;
+                continue;
+            }
+
+            switch (spec) {
+                case 'l':
+                    long_type = true;
+                    break;
+
+                case 'x':
+                    if (long_type)
+                        append_int<uint64_t, 16>(out, count, max, va_arg(va, uint64_t), width, pad);
+                    else
+                        append_int<uint32_t, 16>(out, count, max, va_arg(va, uint32_t), width, pad);
+                    done = true;
+                    break;
+
+                case 'd':
+                case 'u':
+                    if (long_type)
+                        append_int<uint64_t, 10>(out, count, max, va_arg(va, uint64_t), width, pad);
+                    else
+                        append_int<uint32_t, 10>(out, count, max, va_arg(va, uint32_t), width, pad);
+                    done = true;
+                    break;
+
+                case 's':
+                    append_string(out, count, max, va_arg(va, const char *));
+                    done = true;
+                    break;
+            }
+
+            if (done) break;
+            spec = *format++;
+        }
+    }
+
+    return count;
+}
+
+size_t
+format(stringbuf output, const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    size_t result = vformat(output, format, va);
+    va_end(va);
+    return result;
+}
+
+} //namespace util

src/libraries/util/util.module

@@ -4,6 +4,7 @@ module("util",
     kind = "lib",
     sources = [
         "bip_buffer.cpp",
+        "format.cpp",
         "spinlock.cpp",
     ],
     public_headers = [
@@ -13,6 +14,7 @@ module("util",
         "util/counted.h",
         "util/deque.h",
         "util/enum_bitfields.h",
+        "util/format.h",
         "util/hash.h",
         "util/linked_list.h",
         "util/map.h",

src/libraries/util/util/format.h

@@ -0,0 +1,16 @@
+/// \file format.h
+/// sprintf-like format functions
+
+#pragma once
+
+#include <stdarg.h>
+#include <util/counted.h>
+
+namespace util {
+
+using stringbuf = counted<char>;
+
+size_t format(stringbuf output, const char *format, ...);
+size_t vformat(stringbuf output, const char *format, va_list va);
+
+}