py/asmthumb.c - lite/micropython - Linaro Git Browser

 #include <stdint.h>
 #include <stdio.h>
 #include <assert.h>
 #include <string.h>

 #include "misc.h"
 #include "mpconfig.h"
 #include "asmthumb.h"

 // wrapper around everything in this file
 #if MICROPY_EMIT_THUMB || MICROPY_EMIT_INLINE_THUMB

 #define UNSIGNED_FIT8(x) (((x) & 0xffffff00) == 0)
 #define UNSIGNED_FIT16(x) (((x) & 0xffff0000) == 0)
 #define SIGNED_FIT8(x) (((x) & 0xffffff80) == 0) || (((x) & 0xffffff80) == 0xffffff80)
 #define SIGNED_FIT9(x) (((x) & 0xffffff00) == 0) || (((x) & 0xffffff00) == 0xffffff00)
 #define SIGNED_FIT12(x) (((x) & 0xfffff800) == 0) || (((x) & 0xfffff800) == 0xfffff800)

 struct _asm_thumb_t {
     int pass;
     uint code_offset;
     uint code_size;
     byte *code_base;
     byte dummy_data[8];

     int max_num_labels;
     int *label_offsets;
     int num_locals;
     uint push_reglist;
     uint stack_adjust;
 };

 asm_thumb_t *asm_thumb_new(uint max_num_labels) {
     asm_thumb_t *as;

     as = m_new(asm_thumb_t, 1);
     as->pass = 0;
     as->code_offset = 0;
     as->code_size = 0;
     as->code_base = NULL;
     as->max_num_labels = max_num_labels;
     as->label_offsets = m_new(int, max_num_labels);
     as->num_locals = 0;

     return as;
 }

 void asm_thumb_free(asm_thumb_t *as, bool free_code) {
     if (free_code) {
         m_del(byte, as->code_base, as->code_size);
     }
     /*
     if (as->label != NULL) {
         int i;
         for (i = 0; i < as->label->len; ++i)
         {
             Label *lab = &g_array_index(as->label, Label, i);
             if (lab->unresolved != NULL)
                 g_array_free(lab->unresolved, true);
         }
         g_array_free(as->label, true);
     }
     */
     m_del_obj(asm_thumb_t, as);
 }

 void asm_thumb_start_pass(asm_thumb_t *as, int pass) {
     as->pass = pass;
     as->code_offset = 0;
     if (pass == ASM_THUMB_PASS_2) {
         memset(as->label_offsets, -1, as->max_num_labels * sizeof(int));
     }
 }

 void asm_thumb_end_pass(asm_thumb_t *as) {
     if (as->pass == ASM_THUMB_PASS_2) {
         // calculate size of code in bytes
         as->code_size = as->code_offset;
         as->code_base = m_new(byte, as->code_size);
         //printf("code_size: %u\n", as->code_size);
     }

     /*
     // check labels are resolved
     if (as->label != NULL)
     {
         int i;
         for (i = 0; i < as->label->len; ++i)
             if (g_array_index(as->label, Label, i).unresolved != NULL)
                 return false;
     }
     */
 }

 // all functions must go through this one to emit bytes
 STATIC byte *asm_thumb_get_cur_to_write_bytes(asm_thumb_t *as, int num_bytes_to_write) {
     //printf("emit %d\n", num_bytes_to_write);
     if (as->pass < ASM_THUMB_PASS_3) {
         as->code_offset += num_bytes_to_write;
         return as->dummy_data;
     } else {
         assert(as->code_offset + num_bytes_to_write <= as->code_size);
         byte *c = as->code_base + as->code_offset;
         as->code_offset += num_bytes_to_write;
         return c;
     }
 }

 uint asm_thumb_get_code_size(asm_thumb_t *as) {
     return as->code_size;
 }

 void *asm_thumb_get_code(asm_thumb_t *as) {
     // need to set low bit to indicate that it's thumb code
     return (void *)(((machine_uint_t)as->code_base) | 1);
 }

 /*
 STATIC void asm_thumb_write_byte_1(asm_thumb_t *as, byte b1) {
     byte *c = asm_thumb_get_cur_to_write_bytes(as, 1);
     c[0] = b1;
 }
 */

 STATIC void asm_thumb_write_op16(asm_thumb_t *as, uint op) {
     byte *c = asm_thumb_get_cur_to_write_bytes(as, 2);
     // little endian
     c[0] = op;
     c[1] = op >> 8;
 }

 STATIC void asm_thumb_write_op32(asm_thumb_t *as, uint op1, uint op2) {
     byte *c = asm_thumb_get_cur_to_write_bytes(as, 4);
     // little endian, op1 then op2
     c[0] = op1;
     c[1] = op1 >> 8;
     c[2] = op2;
     c[3] = op2 >> 8;
 }

 /*
 #define IMM32_L0(x) ((x) & 0xff)
 #define IMM32_L1(x) (((x) >> 8) & 0xff)
 #define IMM32_L2(x) (((x) >> 16) & 0xff)
 #define IMM32_L3(x) (((x) >> 24) & 0xff)

 STATIC void asm_thumb_write_word32(asm_thumb_t *as, int w32) {
     byte *c = asm_thumb_get_cur_to_write_bytes(as, 4);
     c[0] = IMM32_L0(w32);
     c[1] = IMM32_L1(w32);
     c[2] = IMM32_L2(w32);
     c[3] = IMM32_L3(w32);
 }
 */

 // rlolist is a bit map indicating desired lo-registers
 #define OP_PUSH_RLIST(rlolist)      (0xb400 | (rlolist))
 #define OP_PUSH_RLIST_LR(rlolist)   (0xb400 | 0x0100 | (rlolist))
 #define OP_POP_RLIST(rlolist)       (0xbc00 | (rlolist))
 #define OP_POP_RLIST_PC(rlolist)    (0xbc00 | 0x0100 | (rlolist))

 #define OP_ADD_SP(num_words) (0xb000 | (num_words))
 #define OP_SUB_SP(num_words) (0xb080 | (num_words))

 void asm_thumb_entry(asm_thumb_t *as, int num_locals) {
     // work out what to push and how many extra space to reserve on stack
     // so that we have enough for all locals and it's aligned an 8-byte boundary
     uint reglist;
     uint stack_adjust;
     if (num_locals < 0) {
         num_locals = 0;
     }
     // don't ppop r0 because it's used for return value
     switch (num_locals) {
         case 0:
             reglist = 0xf2;
             stack_adjust = 0;
             break;

         case 1:
             reglist = 0xf2;
             stack_adjust = 0;
             break;

         case 2:
             reglist = 0xfe;
             stack_adjust = 0;
             break;

         case 3:
             reglist = 0xfe;
             stack_adjust = 0;
             break;

         default:
             reglist = 0xfe;
             stack_adjust = ((num_locals - 3) + 1) & (~1);
             break;
     }
     asm_thumb_write_op16(as, OP_PUSH_RLIST_LR(reglist));
     if (stack_adjust > 0) {
         asm_thumb_write_op16(as, OP_SUB_SP(stack_adjust));
     }
     as->push_reglist = reglist;
     as->stack_adjust = stack_adjust;
     as->num_locals = num_locals;
 }

 void asm_thumb_exit(asm_thumb_t *as) {
     if (as->stack_adjust > 0) {
         asm_thumb_write_op16(as, OP_ADD_SP(as->stack_adjust));
     }
     asm_thumb_write_op16(as, OP_POP_RLIST_PC(as->push_reglist));
 }

 void asm_thumb_label_assign(asm_thumb_t *as, int label) {
     assert(label < as->max_num_labels);
     if (as->pass == ASM_THUMB_PASS_2) {
         // assign label offset
         assert(as->label_offsets[label] == -1);
         as->label_offsets[label] = as->code_offset;
     } else if (as->pass == ASM_THUMB_PASS_3) {
         // ensure label offset has not changed from PASS_2 to PASS_3
         //printf("l%d: (at %d=%ld)\n", label, as->label_offsets[label], as->code_offset);
         assert(as->label_offsets[label] == as->code_offset);
     }
 }

 STATIC int get_label_dest(asm_thumb_t *as, int label) {
     assert(label < as->max_num_labels);
     return as->label_offsets[label];
 }

 #define OP_MOVS_RLO_I8(rlo_dest, i8_src) (0x2000 | ((rlo_dest) << 8) | (i8_src))

 // the i8_src value will be zero extended into the r32 register!
 void asm_thumb_movs_rlo_i8(asm_thumb_t *as, uint rlo_dest, int i8_src) {
     assert(rlo_dest < REG_R8);
     // movs rlo_dest, #i8_src
     asm_thumb_write_op16(as, OP_MOVS_RLO_I8(rlo_dest, i8_src));
 }

 #define OP_MOVW (0xf240)
 #define OP_MOVT (0xf2c0)

 // if loading lo half with movw, the i16 value will be zero extended into the r32 register!
 STATIC void asm_thumb_mov_reg_i16(asm_thumb_t *as, uint mov_op, uint reg_dest, int i16_src) {
     assert(reg_dest < REG_R15);
     // mov[wt] reg_dest, #i16_src
     asm_thumb_write_op32(as, mov_op | ((i16_src >> 1) & 0x0400) | ((i16_src >> 12) & 0xf), ((i16_src << 4) & 0x7000) | (reg_dest << 8) | (i16_src & 0xff));
 }

 // the i16_src value will be zero extended into the r32 register!
 void asm_thumb_movw_reg_i16(asm_thumb_t *as, uint reg_dest, int i16_src) {
     asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i16_src);
 }

 // the i16_src value will be zero extended into the r32 register!
 void asm_thumb_movt_reg_i16(asm_thumb_t *as, uint reg_dest, int i16_src) {
     asm_thumb_mov_reg_i16(as, OP_MOVT, reg_dest, i16_src);
 }

 void asm_thumb_mov_reg_reg(asm_thumb_t *as, uint reg_dest, uint reg_src) {
     uint op_lo;
     if (reg_src < 8) {
         op_lo = reg_src << 3;
     } else {
         op_lo = 0x40 | ((reg_src - 8) << 3);
     }
     if (reg_dest < 8) {
         op_lo |= reg_dest;
     } else {
         op_lo |= 0x80 | (reg_dest - 8);
     }
     // mov reg_dest, reg_src
     asm_thumb_write_op16(as, 0x4600 | op_lo);
 }

 #define OP_SUBS_RLO_RLO_I3(rlo_dest, rlo_src, i3_src) (0x1e00 | ((i3_src) << 6) | ((rlo_src) << 3) | (rlo_dest))

 void asm_thumb_subs_rlo_rlo_i3(asm_thumb_t *as, uint rlo_dest, uint rlo_src, int i3_src) {
     assert(rlo_dest < REG_R8);
     assert(rlo_src < REG_R8);
     asm_thumb_write_op16(as, OP_SUBS_RLO_RLO_I3(rlo_dest, rlo_src, i3_src));
 }

 #define OP_CMP_RLO_I8(rlo, i8) (0x2800 | ((rlo) << 8) | (i8))

 void asm_thumb_cmp_rlo_i8(asm_thumb_t *as, uint rlo, int i8) {
     assert(rlo < REG_R8);
     asm_thumb_write_op16(as, OP_CMP_RLO_I8(rlo, i8));
 }

 #define OP_B_N(byte_offset) (0xe000 | (((byte_offset) >> 1) & 0x07ff))

 void asm_thumb_b_n(asm_thumb_t *as, int label) {
     int dest = get_label_dest(as, label);
     int rel = dest - as->code_offset;
     rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
     if (SIGNED_FIT12(rel)) {
         asm_thumb_write_op16(as, OP_B_N(rel));
     } else {
         printf("asm_thumb_b_n: branch does not fit in 12 bits\n");
     }
 }

 #define OP_BCC_N(cond, byte_offset) (0xd000 | ((cond) << 8) | (((byte_offset) >> 1) & 0x00ff))

 void asm_thumb_bcc_n(asm_thumb_t *as, int cond, int label) {
     int dest = get_label_dest(as, label);
     int rel = dest - as->code_offset;
     rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
     if (SIGNED_FIT9(rel)) {
         asm_thumb_write_op16(as, OP_BCC_N(cond, rel));
     } else {
         printf("asm_thumb_bcc_n: branch does not fit in 9 bits\n");
     }
 }

 void asm_thumb_mov_reg_i32(asm_thumb_t *as, uint reg_dest, machine_uint_t i32) {
     // movw, movt does it in 8 bytes
     // ldr [pc, #], dw does it in 6 bytes, but we might not reach to end of code for dw

     asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i32);
     asm_thumb_mov_reg_i16(as, OP_MOVT, reg_dest, i32 >> 16);
 }

 void asm_thumb_mov_reg_i32_optimised(asm_thumb_t *as, uint reg_dest, int i32) {
     if (reg_dest < 8 && UNSIGNED_FIT8(i32)) {
         asm_thumb_movs_rlo_i8(as, reg_dest, i32);
     } else if (UNSIGNED_FIT16(i32)) {
         asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i32);
     } else {
         asm_thumb_mov_reg_i32(as, reg_dest, i32);
     }
 }

 #define OP_STR_TO_SP_OFFSET(rlo_dest, word_offset) (0x9000 | ((rlo_dest) << 8) | ((word_offset) & 0x00ff))
 #define OP_LDR_FROM_SP_OFFSET(rlo_dest, word_offset) (0x9800 | ((rlo_dest) << 8) | ((word_offset) & 0x00ff))

 void asm_thumb_mov_local_reg(asm_thumb_t *as, int local_num, uint rlo_src) {
     assert(rlo_src < REG_R8);
     int word_offset = as->num_locals - local_num - 1;
     assert(as->pass < ASM_THUMB_PASS_3 || word_offset >= 0);
     asm_thumb_write_op16(as, OP_STR_TO_SP_OFFSET(rlo_src, word_offset));
 }

 void asm_thumb_mov_reg_local(asm_thumb_t *as, uint rlo_dest, int local_num) {
     assert(rlo_dest < REG_R8);
     int word_offset = as->num_locals - local_num - 1;
     assert(as->pass < ASM_THUMB_PASS_3 || word_offset >= 0);
     asm_thumb_write_op16(as, OP_LDR_FROM_SP_OFFSET(rlo_dest, word_offset));
 }

 #define OP_ADD_REG_SP_OFFSET(rlo_dest, word_offset) (0xa800 | ((rlo_dest) << 8) | ((word_offset) & 0x00ff))

 void asm_thumb_mov_reg_local_addr(asm_thumb_t *as, uint rlo_dest, int local_num) {
     assert(rlo_dest < REG_R8);
     int word_offset = as->num_locals - local_num - 1;
     assert(as->pass < ASM_THUMB_PASS_3 || word_offset >= 0);
     asm_thumb_write_op16(as, OP_ADD_REG_SP_OFFSET(rlo_dest, word_offset));
 }

 #define OP_ADD_REG_REG_REG(rlo_dest, rlo_src_a, rlo_src_b) (0x1800 | ((rlo_src_b) << 6) | ((rlo_src_a) << 3) | (rlo_dest))

 void asm_thumb_add_reg_reg_reg(asm_thumb_t *as, uint rlo_dest, uint rlo_src_a, uint rlo_src_b) {
     asm_thumb_write_op16(as, OP_ADD_REG_REG_REG(rlo_dest, rlo_src_a, rlo_src_b));
 }

 #define OP_CMP_REG_REG(rlo_a, rlo_b) (0x4280 | ((rlo_b) << 3) | (rlo_a))

 void asm_thumb_cmp_reg_reg(asm_thumb_t *as, uint rlo_a, uint rlo_b) {
     asm_thumb_write_op16(as, OP_CMP_REG_REG(rlo_a, rlo_b));
 }

 void asm_thumb_ite_ge(asm_thumb_t *as) {
     asm_thumb_write_op16(as, 0xbfac);
 }

 // this could be wrong, because it should have a range of +/- 16MiB...
 #define OP_BW_HI(byte_offset) (0xf000 | (((byte_offset) >> 12) & 0x07ff))
 #define OP_BW_LO(byte_offset) (0xb800 | (((byte_offset) >> 1) & 0x07ff))

 void asm_thumb_b_label(asm_thumb_t *as, int label) {
     int dest = get_label_dest(as, label);
     int rel = dest - as->code_offset;
     rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
     if (dest >= 0 && rel <= -4) {
         // is a backwards jump, so we know the size of the jump on the first pass
         // calculate rel assuming 12 bit relative jump
         if (SIGNED_FIT12(rel)) {
             asm_thumb_write_op16(as, OP_B_N(rel));
         } else {
             goto large_jump;
         }
     } else {
         // is a forwards jump, so need to assume it's large
         large_jump:
         asm_thumb_write_op32(as, OP_BW_HI(rel), OP_BW_LO(rel));
     }
 }

 // all these bit arithmetics need coverage testing!
 #define OP_BCC_W_HI(cond, byte_offset) (0xf000 | ((cond) << 6) | (((byte_offset) >> 10) & 0x0400) | (((byte_offset) >> 14) & 0x003f))
 #define OP_BCC_W_LO(byte_offset) (0x8000 | ((byte_offset) & 0x2000) | (((byte_offset) >> 1) & 0x0fff))

 void asm_thumb_bcc_label(asm_thumb_t *as, int cond, int label) {
     int dest = get_label_dest(as, label);
     int rel = dest - as->code_offset;
     rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
     if (dest >= 0 && rel <= -4) {
         // is a backwards jump, so we know the size of the jump on the first pass
         // calculate rel assuming 9 bit relative jump
         if (SIGNED_FIT9(rel)) {
             asm_thumb_write_op16(as, OP_BCC_N(cond, rel));
         } else {
             goto large_jump;
         }
     } else {
         // is a forwards jump, so need to assume it's large
         large_jump:
         asm_thumb_write_op32(as, OP_BCC_W_HI(cond, rel), OP_BCC_W_LO(rel));
     }
 }

 #define OP_BLX(reg) (0x4780 | ((reg) << 3))
 #define OP_SVC(arg) (0xdf00 | (arg))
 #define OP_LDR_FROM_BASE_OFFSET(rlo_dest, rlo_base, word_offset) (0x6800 | (((word_offset) << 6) & 0x07c0) | ((rlo_base) << 3) | (rlo_dest))

 void asm_thumb_bl_ind(asm_thumb_t *as, void *fun_ptr, uint fun_id, uint reg_temp) {
     /* TODO make this use less bytes
     uint rlo_base = REG_R3;
     uint rlo_dest = REG_R7;
     uint word_offset = 4;
     asm_thumb_write_op16(as, 0x0000);
     asm_thumb_write_op16(as, 0x6800 | (word_offset << 6) | (rlo_base << 3) | rlo_dest); // ldr rlo_dest, [rlo_base, #offset]
     asm_thumb_write_op16(as, 0x4780 | (REG_R9 << 3)); // blx reg
     */

     if (0) {
         // load ptr to function into register using immediate, then branch
         // not relocatable
         asm_thumb_mov_reg_i32(as, reg_temp, (machine_uint_t)fun_ptr);
         asm_thumb_write_op16(as, OP_BLX(reg_temp));
     } else if (1) {
         asm_thumb_write_op16(as, OP_LDR_FROM_BASE_OFFSET(reg_temp, REG_R7, fun_id));
         asm_thumb_write_op16(as, OP_BLX(reg_temp));
     } else {
         // use SVC
         asm_thumb_write_op16(as, OP_SVC(fun_id));
     }
 }

 #endif // MICROPY_EMIT_THUMB || MICROPY_EMIT_INLINE_THUMB
	#include <stdint.h>
	#include <stdio.h>
	#include <assert.h>
	#include <string.h>

	#include "misc.h"
	#include "mpconfig.h"
	#include "asmthumb.h"

	// wrapper around everything in this file
	#if MICROPY_EMIT_THUMB \|\| MICROPY_EMIT_INLINE_THUMB

	#define UNSIGNED_FIT8(x) (((x) & 0xffffff00) == 0)
	#define UNSIGNED_FIT16(x) (((x) & 0xffff0000) == 0)
	#define SIGNED_FIT8(x) (((x) & 0xffffff80) == 0) \|\| (((x) & 0xffffff80) == 0xffffff80)
	#define SIGNED_FIT9(x) (((x) & 0xffffff00) == 0) \|\| (((x) & 0xffffff00) == 0xffffff00)
	#define SIGNED_FIT12(x) (((x) & 0xfffff800) == 0) \|\| (((x) & 0xfffff800) == 0xfffff800)

	struct _asm_thumb_t {
	int pass;
	uint code_offset;
	uint code_size;
	byte *code_base;
	byte dummy_data[8];

	int max_num_labels;
	int *label_offsets;
	int num_locals;
	uint push_reglist;
	uint stack_adjust;
	};

	asm_thumb_t *asm_thumb_new(uint max_num_labels) {
	asm_thumb_t *as;

	as = m_new(asm_thumb_t, 1);
	as->pass = 0;
	as->code_offset = 0;
	as->code_size = 0;
	as->code_base = NULL;
	as->max_num_labels = max_num_labels;
	as->label_offsets = m_new(int, max_num_labels);
	as->num_locals = 0;

	return as;
	}

	void asm_thumb_free(asm_thumb_t *as, bool free_code) {
	if (free_code) {
	m_del(byte, as->code_base, as->code_size);
	}
	/*
	if (as->label != NULL) {
	int i;
	for (i = 0; i < as->label->len; ++i)
	{
	Label *lab = &g_array_index(as->label, Label, i);
	if (lab->unresolved != NULL)
	g_array_free(lab->unresolved, true);
	}
	g_array_free(as->label, true);
	}
	*/
	m_del_obj(asm_thumb_t, as);
	}

	void asm_thumb_start_pass(asm_thumb_t *as, int pass) {
	as->pass = pass;
	as->code_offset = 0;
	if (pass == ASM_THUMB_PASS_2) {
	memset(as->label_offsets, -1, as->max_num_labels * sizeof(int));
	}
	}

	void asm_thumb_end_pass(asm_thumb_t *as) {
	if (as->pass == ASM_THUMB_PASS_2) {
	// calculate size of code in bytes
	as->code_size = as->code_offset;
	as->code_base = m_new(byte, as->code_size);
	//printf("code_size: %u\n", as->code_size);
	}

	/*
	// check labels are resolved
	if (as->label != NULL)
	{
	int i;
	for (i = 0; i < as->label->len; ++i)
	if (g_array_index(as->label, Label, i).unresolved != NULL)
	return false;
	}
	*/
	}

	// all functions must go through this one to emit bytes
	STATIC byte asm_thumb_get_cur_to_write_bytes(asm_thumb_t as, int num_bytes_to_write) {
	//printf("emit %d\n", num_bytes_to_write);
	if (as->pass < ASM_THUMB_PASS_3) {
	as->code_offset += num_bytes_to_write;
	return as->dummy_data;
	} else {
	assert(as->code_offset + num_bytes_to_write <= as->code_size);
	byte *c = as->code_base + as->code_offset;
	as->code_offset += num_bytes_to_write;
	return c;
	}
	}

	uint asm_thumb_get_code_size(asm_thumb_t *as) {
	return as->code_size;
	}

	void asm_thumb_get_code(asm_thumb_t as) {
	// need to set low bit to indicate that it's thumb code
	return (void *)(((machine_uint_t)as->code_base) \| 1);
	}

	/*
	STATIC void asm_thumb_write_byte_1(asm_thumb_t *as, byte b1) {
	byte *c = asm_thumb_get_cur_to_write_bytes(as, 1);
	c[0] = b1;
	}
	*/

	STATIC void asm_thumb_write_op16(asm_thumb_t *as, uint op) {
	byte *c = asm_thumb_get_cur_to_write_bytes(as, 2);
	// little endian
	c[0] = op;
	c[1] = op >> 8;
	}

	STATIC void asm_thumb_write_op32(asm_thumb_t *as, uint op1, uint op2) {
	byte *c = asm_thumb_get_cur_to_write_bytes(as, 4);
	// little endian, op1 then op2
	c[0] = op1;
	c[1] = op1 >> 8;
	c[2] = op2;
	c[3] = op2 >> 8;
	}

	/*
	#define IMM32_L0(x) ((x) & 0xff)
	#define IMM32_L1(x) (((x) >> 8) & 0xff)
	#define IMM32_L2(x) (((x) >> 16) & 0xff)
	#define IMM32_L3(x) (((x) >> 24) & 0xff)

	STATIC void asm_thumb_write_word32(asm_thumb_t *as, int w32) {
	byte *c = asm_thumb_get_cur_to_write_bytes(as, 4);
	c[0] = IMM32_L0(w32);
	c[1] = IMM32_L1(w32);
	c[2] = IMM32_L2(w32);
	c[3] = IMM32_L3(w32);
	}
	*/

	// rlolist is a bit map indicating desired lo-registers
	#define OP_PUSH_RLIST(rlolist) (0xb400 \| (rlolist))
	#define OP_PUSH_RLIST_LR(rlolist) (0xb400 \| 0x0100 \| (rlolist))
	#define OP_POP_RLIST(rlolist) (0xbc00 \| (rlolist))
	#define OP_POP_RLIST_PC(rlolist) (0xbc00 \| 0x0100 \| (rlolist))

	#define OP_ADD_SP(num_words) (0xb000 \| (num_words))
	#define OP_SUB_SP(num_words) (0xb080 \| (num_words))

	void asm_thumb_entry(asm_thumb_t *as, int num_locals) {
	// work out what to push and how many extra space to reserve on stack
	// so that we have enough for all locals and it's aligned an 8-byte boundary
	uint reglist;
	uint stack_adjust;
	if (num_locals < 0) {
	num_locals = 0;
	}
	// don't ppop r0 because it's used for return value
	switch (num_locals) {
	case 0:
	reglist = 0xf2;
	stack_adjust = 0;
	break;

	case 1:
	reglist = 0xf2;
	stack_adjust = 0;
	break;

	case 2:
	reglist = 0xfe;
	stack_adjust = 0;
	break;

	case 3:
	reglist = 0xfe;
	stack_adjust = 0;
	break;

	default:
	reglist = 0xfe;
	stack_adjust = ((num_locals - 3) + 1) & (~1);
	break;
	}
	asm_thumb_write_op16(as, OP_PUSH_RLIST_LR(reglist));
	if (stack_adjust > 0) {
	asm_thumb_write_op16(as, OP_SUB_SP(stack_adjust));
	}
	as->push_reglist = reglist;
	as->stack_adjust = stack_adjust;
	as->num_locals = num_locals;
	}

	void asm_thumb_exit(asm_thumb_t *as) {
	if (as->stack_adjust > 0) {
	asm_thumb_write_op16(as, OP_ADD_SP(as->stack_adjust));
	}
	asm_thumb_write_op16(as, OP_POP_RLIST_PC(as->push_reglist));
	}

	void asm_thumb_label_assign(asm_thumb_t *as, int label) {
	assert(label < as->max_num_labels);
	if (as->pass == ASM_THUMB_PASS_2) {
	// assign label offset
	assert(as->label_offsets[label] == -1);
	as->label_offsets[label] = as->code_offset;
	} else if (as->pass == ASM_THUMB_PASS_3) {
	// ensure label offset has not changed from PASS_2 to PASS_3
	//printf("l%d: (at %d=%ld)\n", label, as->label_offsets[label], as->code_offset);
	assert(as->label_offsets[label] == as->code_offset);
	}
	}

	STATIC int get_label_dest(asm_thumb_t *as, int label) {
	assert(label < as->max_num_labels);
	return as->label_offsets[label];
	}

	#define OP_MOVS_RLO_I8(rlo_dest, i8_src) (0x2000 \| ((rlo_dest) << 8) \| (i8_src))

	// the i8_src value will be zero extended into the r32 register!
	void asm_thumb_movs_rlo_i8(asm_thumb_t *as, uint rlo_dest, int i8_src) {
	assert(rlo_dest < REG_R8);
	// movs rlo_dest, #i8_src
	asm_thumb_write_op16(as, OP_MOVS_RLO_I8(rlo_dest, i8_src));
	}

	#define OP_MOVW (0xf240)
	#define OP_MOVT (0xf2c0)

	// if loading lo half with movw, the i16 value will be zero extended into the r32 register!
	STATIC void asm_thumb_mov_reg_i16(asm_thumb_t *as, uint mov_op, uint reg_dest, int i16_src) {
	assert(reg_dest < REG_R15);
	// mov[wt] reg_dest, #i16_src
	asm_thumb_write_op32(as, mov_op \| ((i16_src >> 1) & 0x0400) \| ((i16_src >> 12) & 0xf), ((i16_src << 4) & 0x7000) \| (reg_dest << 8) \| (i16_src & 0xff));
	}

	// the i16_src value will be zero extended into the r32 register!
	void asm_thumb_movw_reg_i16(asm_thumb_t *as, uint reg_dest, int i16_src) {
	asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i16_src);
	}

	// the i16_src value will be zero extended into the r32 register!
	void asm_thumb_movt_reg_i16(asm_thumb_t *as, uint reg_dest, int i16_src) {
	asm_thumb_mov_reg_i16(as, OP_MOVT, reg_dest, i16_src);
	}

	void asm_thumb_mov_reg_reg(asm_thumb_t *as, uint reg_dest, uint reg_src) {
	uint op_lo;
	if (reg_src < 8) {
	op_lo = reg_src << 3;
	} else {
	op_lo = 0x40 \| ((reg_src - 8) << 3);
	}
	if (reg_dest < 8) {
	op_lo \|= reg_dest;
	} else {
	op_lo \|= 0x80 \| (reg_dest - 8);
	}
	// mov reg_dest, reg_src
	asm_thumb_write_op16(as, 0x4600 \| op_lo);
	}

	#define OP_SUBS_RLO_RLO_I3(rlo_dest, rlo_src, i3_src) (0x1e00 \| ((i3_src) << 6) \| ((rlo_src) << 3) \| (rlo_dest))

	void asm_thumb_subs_rlo_rlo_i3(asm_thumb_t *as, uint rlo_dest, uint rlo_src, int i3_src) {
	assert(rlo_dest < REG_R8);
	assert(rlo_src < REG_R8);
	asm_thumb_write_op16(as, OP_SUBS_RLO_RLO_I3(rlo_dest, rlo_src, i3_src));
	}

	#define OP_CMP_RLO_I8(rlo, i8) (0x2800 \| ((rlo) << 8) \| (i8))

	void asm_thumb_cmp_rlo_i8(asm_thumb_t *as, uint rlo, int i8) {
	assert(rlo < REG_R8);
	asm_thumb_write_op16(as, OP_CMP_RLO_I8(rlo, i8));
	}

	#define OP_B_N(byte_offset) (0xe000 \| (((byte_offset) >> 1) & 0x07ff))

	void asm_thumb_b_n(asm_thumb_t *as, int label) {
	int dest = get_label_dest(as, label);
	int rel = dest - as->code_offset;
	rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
	if (SIGNED_FIT12(rel)) {
	asm_thumb_write_op16(as, OP_B_N(rel));
	} else {
	printf("asm_thumb_b_n: branch does not fit in 12 bits\n");
	}
	}

	#define OP_BCC_N(cond, byte_offset) (0xd000 \| ((cond) << 8) \| (((byte_offset) >> 1) & 0x00ff))

	void asm_thumb_bcc_n(asm_thumb_t *as, int cond, int label) {
	int dest = get_label_dest(as, label);
	int rel = dest - as->code_offset;
	rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
	if (SIGNED_FIT9(rel)) {
	asm_thumb_write_op16(as, OP_BCC_N(cond, rel));
	} else {
	printf("asm_thumb_bcc_n: branch does not fit in 9 bits\n");
	}
	}

	void asm_thumb_mov_reg_i32(asm_thumb_t *as, uint reg_dest, machine_uint_t i32) {
	// movw, movt does it in 8 bytes
	// ldr [pc, #], dw does it in 6 bytes, but we might not reach to end of code for dw

	asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i32);
	asm_thumb_mov_reg_i16(as, OP_MOVT, reg_dest, i32 >> 16);
	}

	void asm_thumb_mov_reg_i32_optimised(asm_thumb_t *as, uint reg_dest, int i32) {
	if (reg_dest < 8 && UNSIGNED_FIT8(i32)) {
	asm_thumb_movs_rlo_i8(as, reg_dest, i32);
	} else if (UNSIGNED_FIT16(i32)) {
	asm_thumb_mov_reg_i16(as, OP_MOVW, reg_dest, i32);
	} else {
	asm_thumb_mov_reg_i32(as, reg_dest, i32);
	}
	}

	#define OP_STR_TO_SP_OFFSET(rlo_dest, word_offset) (0x9000 \| ((rlo_dest) << 8) \| ((word_offset) & 0x00ff))
	#define OP_LDR_FROM_SP_OFFSET(rlo_dest, word_offset) (0x9800 \| ((rlo_dest) << 8) \| ((word_offset) & 0x00ff))

	void asm_thumb_mov_local_reg(asm_thumb_t *as, int local_num, uint rlo_src) {
	assert(rlo_src < REG_R8);
	int word_offset = as->num_locals - local_num - 1;
	assert(as->pass < ASM_THUMB_PASS_3 \|\| word_offset >= 0);
	asm_thumb_write_op16(as, OP_STR_TO_SP_OFFSET(rlo_src, word_offset));
	}

	void asm_thumb_mov_reg_local(asm_thumb_t *as, uint rlo_dest, int local_num) {
	assert(rlo_dest < REG_R8);
	int word_offset = as->num_locals - local_num - 1;
	assert(as->pass < ASM_THUMB_PASS_3 \|\| word_offset >= 0);
	asm_thumb_write_op16(as, OP_LDR_FROM_SP_OFFSET(rlo_dest, word_offset));
	}

	#define OP_ADD_REG_SP_OFFSET(rlo_dest, word_offset) (0xa800 \| ((rlo_dest) << 8) \| ((word_offset) & 0x00ff))

	void asm_thumb_mov_reg_local_addr(asm_thumb_t *as, uint rlo_dest, int local_num) {
	assert(rlo_dest < REG_R8);
	int word_offset = as->num_locals - local_num - 1;
	assert(as->pass < ASM_THUMB_PASS_3 \|\| word_offset >= 0);
	asm_thumb_write_op16(as, OP_ADD_REG_SP_OFFSET(rlo_dest, word_offset));
	}

	#define OP_ADD_REG_REG_REG(rlo_dest, rlo_src_a, rlo_src_b) (0x1800 \| ((rlo_src_b) << 6) \| ((rlo_src_a) << 3) \| (rlo_dest))

	void asm_thumb_add_reg_reg_reg(asm_thumb_t *as, uint rlo_dest, uint rlo_src_a, uint rlo_src_b) {
	asm_thumb_write_op16(as, OP_ADD_REG_REG_REG(rlo_dest, rlo_src_a, rlo_src_b));
	}

	#define OP_CMP_REG_REG(rlo_a, rlo_b) (0x4280 \| ((rlo_b) << 3) \| (rlo_a))

	void asm_thumb_cmp_reg_reg(asm_thumb_t *as, uint rlo_a, uint rlo_b) {
	asm_thumb_write_op16(as, OP_CMP_REG_REG(rlo_a, rlo_b));
	}

	void asm_thumb_ite_ge(asm_thumb_t *as) {
	asm_thumb_write_op16(as, 0xbfac);
	}

	// this could be wrong, because it should have a range of +/- 16MiB...
	#define OP_BW_HI(byte_offset) (0xf000 \| (((byte_offset) >> 12) & 0x07ff))
	#define OP_BW_LO(byte_offset) (0xb800 \| (((byte_offset) >> 1) & 0x07ff))

	void asm_thumb_b_label(asm_thumb_t *as, int label) {
	int dest = get_label_dest(as, label);
	int rel = dest - as->code_offset;
	rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
	if (dest >= 0 && rel <= -4) {
	// is a backwards jump, so we know the size of the jump on the first pass
	// calculate rel assuming 12 bit relative jump
	if (SIGNED_FIT12(rel)) {
	asm_thumb_write_op16(as, OP_B_N(rel));
	} else {
	goto large_jump;
	}
	} else {
	// is a forwards jump, so need to assume it's large
	large_jump:
	asm_thumb_write_op32(as, OP_BW_HI(rel), OP_BW_LO(rel));
	}
	}

	// all these bit arithmetics need coverage testing!
	#define OP_BCC_W_HI(cond, byte_offset) (0xf000 \| ((cond) << 6) \| (((byte_offset) >> 10) & 0x0400) \| (((byte_offset) >> 14) & 0x003f))
	#define OP_BCC_W_LO(byte_offset) (0x8000 \| ((byte_offset) & 0x2000) \| (((byte_offset) >> 1) & 0x0fff))

	void asm_thumb_bcc_label(asm_thumb_t *as, int cond, int label) {
	int dest = get_label_dest(as, label);
	int rel = dest - as->code_offset;
	rel -= 4; // account for instruction prefetch, PC is 4 bytes ahead of this instruction
	if (dest >= 0 && rel <= -4) {
	// is a backwards jump, so we know the size of the jump on the first pass
	// calculate rel assuming 9 bit relative jump
	if (SIGNED_FIT9(rel)) {
	asm_thumb_write_op16(as, OP_BCC_N(cond, rel));
	} else {
	goto large_jump;
	}
	} else {
	// is a forwards jump, so need to assume it's large
	large_jump:
	asm_thumb_write_op32(as, OP_BCC_W_HI(cond, rel), OP_BCC_W_LO(rel));
	}
	}

	#define OP_BLX(reg) (0x4780 \| ((reg) << 3))
	#define OP_SVC(arg) (0xdf00 \| (arg))
	#define OP_LDR_FROM_BASE_OFFSET(rlo_dest, rlo_base, word_offset) (0x6800 \| (((word_offset) << 6) & 0x07c0) \| ((rlo_base) << 3) \| (rlo_dest))

	void asm_thumb_bl_ind(asm_thumb_t as, void fun_ptr, uint fun_id, uint reg_temp) {
	/* TODO make this use less bytes
	uint rlo_base = REG_R3;
	uint rlo_dest = REG_R7;
	uint word_offset = 4;
	asm_thumb_write_op16(as, 0x0000);
	asm_thumb_write_op16(as, 0x6800 \| (word_offset << 6) \| (rlo_base << 3) \| rlo_dest); // ldr rlo_dest, [rlo_base, #offset]
	asm_thumb_write_op16(as, 0x4780 \| (REG_R9 << 3)); // blx reg
	*/

	if (0) {
	// load ptr to function into register using immediate, then branch
	// not relocatable
	asm_thumb_mov_reg_i32(as, reg_temp, (machine_uint_t)fun_ptr);
	asm_thumb_write_op16(as, OP_BLX(reg_temp));
	} else if (1) {
	asm_thumb_write_op16(as, OP_LDR_FROM_BASE_OFFSET(reg_temp, REG_R7, fun_id));
	asm_thumb_write_op16(as, OP_BLX(reg_temp));
	} else {
	// use SVC
	asm_thumb_write_op16(as, OP_SVC(fun_id));
	}
	}

	#endif // MICROPY_EMIT_THUMB \|\| MICROPY_EMIT_INLINE_THUMB