1 files changed, 124 insertions, 0 deletions
diff --git a/lib/libc-headless/stdio/sprintf.c b/lib/libc-headless/stdio/sprintf.c
new file mode 100644
index 0000000..2881bd5
--- /dev/null
+++ b/lib/libc-headless/stdio/sprintf.c
@@ -0,0 +1,124 @@
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <ctype.h>
+
+#define VSNPRINTF_PUTC(c) if(size > written) str[written++] = c; else written++
+
+int
+vsnprintf(char *restrict str, size_t size, const char *restrict format, va_list ap)
+{
+    int written = 0;
+    for(int fmti = 0; format[fmti] != 0; fmti++) {
+        char fmtc = format[fmti];
+        if(fmtc != '%') {
+            VSNPRINTF_PUTC(fmtc);
+            continue;
+        }
+
+        /* Flags */
+        bool alternate = false;
+        bool zeropad = false;
+        bool leftadj = false;
+        bool signspace = false;
+        bool showplus = false;
+        fmtc = format[++fmti];
+        
+        switch(fmtc) {
+            case '#': alternate = true; fmti++; break;
+            case '0': zeropad = true; fmti++; break;
+            case '-': leftadj = true; fmti++; break;
+            case ' ': signspace = true; fmti++; break;
+            case '+': showplus = true; fmti++; break;
+            default: break;
+        }
+
+        /* Field width. */
+        fmtc = format[fmti];
+        //TODO: Implement field width
+
+        /* Precision. */
+        fmtc = format[fmti];
+        //TODO: Implement precision
+    
+        /* Length modifier */
+        fmtc = format[fmti];
+        //TODO: Implement length modifier.
+
+        /* Conversion specifier. */
+        bool is_signed = true;
+        bool is_caps = false;
+        int radix = 10;
+        fmtc = format[fmti];
+        switch(fmtc)
+        {
+            case 'X':
+                is_caps = true;
+            case 'x':
+                radix = 16;
+            case 'u':
+                is_signed = false;
+            case 'd':
+            case 'i':
+                goto conversion_int;
+           case 'p':
+                alternate = true;
+                radix = 16;
+                is_signed = false;
+                is_caps = true;
+                goto conversion_int;
+            case '%':
+                VSNPRINTF_PUTC('%');
+                break;
+        }
+        continue;
+
+conversion_int:
+        {
+            uintmax_t value = va_arg(ap, uintmax_t);
+            bool negative = is_signed && (intmax_t)value < 0;
+            if(negative) value = (uintmax_t)(-(intmax_t)value);
+            size_t numc = 0;
+
+            /*Count the number of characters to put in the buffer to represent
+             * the value in ASCII.*/
+            for(uintmax_t v = value; v != 0; v /= radix, numc++);
+            if(numc == 0) numc++;
+
+            /* Reserve space for alternate repersentation.*/
+            if(showplus && !negative) { VSNPRINTF_PUTC('+'); }
+            if(negative) { VSNPRINTF_PUTC('-'); }
+            if(signspace && !negative) { VSNPRINTF_PUTC(' '); }
+            if(alternate) {
+                VSNPRINTF_PUTC('0');
+                if(radix == 16) {
+                    VSNPRINTF_PUTC('x');
+                }
+                if(alternate && radix == 2) {
+                    VSNPRINTF_PUTC('b');
+                }
+            }
+
+            /* Try to put characters into the buffer*/
+            if(value == 0) {
+                VSNPRINTF_PUTC('0');
+            }
+            else {
+                for(uintmax_t v = value, i = numc - 1; v != 0; v /= radix, i--) {
+                    if(written + i >= size) continue;
+                    int digit = v % radix;
+                    char c = digit > 10 ? (digit + 'a' - 10) : (digit + '0');
+                    if(is_caps) c = toupper(c);
+                    str[written + i] = c;
+                }
+                written += numc;
+            }
+            continue;
+        }
+    }
+    VSNPRINTF_PUTC(0);
+    return written - 1;
+}
+
+