text_blit.S

.syntax unified
.cpu cortex-m0plus
.thumb

#ifndef FONT_BLIT_UNROLL
#define FONT_BLIT_UNROLL 4
#endif

.macro decl_func name
.global \name
.type \name,%function
.thumb_func
\name:
.endm

.altmacro
.macro for_loop count body
.set i, 0
.rept \count
	body %i
	.set i,i+1
.endr
.endm

.macro font8_blit_body i
	ldrb r2, [r1, #\i]
	lsls r2, #5 // 8px font, 4 byte/pix
	adds r2, r3
	ldmia r2!, {r4-r7}
	stmia r0!, {r4-r7}
	ldmia r2!, {r4-r7}
	stmia r0!, {r4-r7}
.endm

// r0: dst
// r1: src
// r2: len in characters
// r3: font line pointer

decl_func font8_blit
	push {r4-r7, lr}
	adds r2, r1
	mov ip, r2
	b 2f
1:
	for_loop FONT_BLIT_UNROLL font8_blit_body
	adds r1, #FONT_BLIT_UNROLL
2:
	cmp r1, ip
	blo 1b
	pop {r4-r7, pc}