modstruct: Initial implementation of struct.pack().

py/binary.c

@@ -138,6 +138,45 @@ mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr) {
     }
 }
 
+void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **ptr) {
+    byte *p = *ptr;
+    uint align;
+
+    int size = mp_binary_get_size(struct_type, val_type, &align);
+    if (struct_type == '@') {
+        // Make pointer aligned
+        p = (byte*)(((machine_uint_t)p + align - 1) & ~(align - 1));
+        #if MP_ENDIANNESS_LITTLE
+        struct_type = '<';
+        #else
+        struct_type = '>';
+        #endif
+    }
+
+#if MP_ENDIANNESS_BIG
+#error Not implemented
+#endif
+    machine_int_t val = mp_obj_int_get_checked(val_in);
+    byte *in = (byte*)&val;
+    int in_delta, out_delta;
+    uint val_sz = MIN(size, sizeof(val));
+    if (struct_type == '>') {
+        in_delta = -1;
+        out_delta = 1;
+        in += val_sz - 1;
+    } else {
+        in_delta = out_delta = 1;
+    }
+
+    for (uint i = val_sz; i > 0; i--) {
+        *p = *in;
+        p += out_delta;
+        in += in_delta;
+    }
+
+    *ptr += size;
+}
+
 void mp_binary_set_val_array(char typecode, void *p, int index, mp_obj_t val_in) {
     switch (typecode) {
 #if MICROPY_ENABLE_FLOAT

py/binary.h

@@ -4,6 +4,7 @@
 
 int mp_binary_get_size(char struct_type, char val_type, uint *palign);
 mp_obj_t mp_binary_get_val_array(char typecode, void *p, int index);
-mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr);
 void mp_binary_set_val_array(char typecode, void *p, int index, mp_obj_t val_in);
 void mp_binary_set_val_array_from_int(char typecode, void *p, int index, machine_int_t val);
+mp_obj_t mp_binary_get_val(char struct_type, char val_type, byte **ptr);
+void mp_binary_set_val(char struct_type, char val_type, mp_obj_t val_in, byte **ptr);

py/modstruct.c

@@ -6,6 +6,7 @@
 #include "obj.h"
 #include "builtin.h"
 #include "objtuple.h"
+#include "objstr.h"
 #include "binary.h"
 
 #if MICROPY_ENABLE_MOD_STRUCT
@@ -69,9 +70,26 @@ STATIC mp_obj_t struct_unpack(mp_obj_t fmt_in, mp_obj_t data_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_2(struct_unpack_obj, struct_unpack);
 
+STATIC mp_obj_t struct_pack(uint n_args, mp_obj_t *args) {
+    // TODO: "The arguments must match the values required by the format exactly."
+    const char *fmt = mp_obj_str_get_str(args[0]);
+    char fmt_type = get_fmt_type(&fmt);
+    int size = MP_OBJ_SMALL_INT_VALUE(struct_calcsize(args[0]));
+    byte *p;
+    mp_obj_t res = mp_obj_str_builder_start(&mp_type_bytes, size, &p);
+    memset(p, 0, size);
+
+    for (uint i = 1; i < n_args; i++) {
+        mp_binary_set_val(fmt_type, *fmt++, args[i], &p);
+    }
+    return res;
+}
+MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(struct_pack_obj, 1, -1, struct_pack);
+
 STATIC const mp_map_elem_t mp_module_struct_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_struct) },
     { MP_OBJ_NEW_QSTR(MP_QSTR_calcsize), (mp_obj_t)&struct_calcsize_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_pack), (mp_obj_t)&struct_pack_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_unpack), (mp_obj_t)&struct_unpack_obj },
 };
 

py/qstrdefs.h

@@ -139,16 +139,10 @@ Q(staticmethod)
 Q(sum)
 Q(super)
 Q(str)
-#if MICROPY_ENABLE_MOD_STRUCT
-Q(struct)
-#endif
 Q(sys)
 Q(to_bytes)
 Q(tuple)
 Q(type)
-#if MICROPY_ENABLE_MOD_STRUCT
-Q(unpack)
-#endif
 Q(value)
 Q(zip)
 
@@ -299,6 +293,12 @@ Q(version)
 Q(version_info)
 #endif
 
+#if MICROPY_ENABLE_MOD_STRUCT
+Q(struct)
+Q(pack)
+Q(unpack)
+#endif
+
 #if MICROPY_ENABLE_PROPERTY
 Q(property)
 Q(getter)

tests/basics/struct1.py

@@ -6,3 +6,13 @@ print(struct.unpack(">bI", b"\x80\0\0\x01\0"))
 
 # 32-bit little-endian specific
 #print(struct.unpack("bI", b"\x80\xaa\x55\xaa\0\0\x01\0"))
+
+print(struct.pack("<i", 1))
+print(struct.pack(">i", 1))
+print(struct.pack("<h", 1))
+print(struct.pack(">h", 1))
+print(struct.pack("<b", 1))
+print(struct.pack(">b", 1))
+
+print(struct.pack("<bI", -128, 256))
+print(struct.pack(">bI", -128, 256))