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Merge pull request #14 from Pharap/master 

Fix bug in drawPixel asm
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Scott Allen 2017-06-16 17:59:03 -04:00 committed by GitHub
parent 342186281a 427c1d53f2
commit 6074f9fc56
1 changed files with 6 additions and 5 deletions
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11
src/Arduboy2.cpp
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@ -299,24 +299,25 @@ void Arduboy2Base::drawPixel(int16_t x, int16_t y, uint8_t color)
// the above math can also be rewritten more simply as;
// row_offset = (y * WIDTH/8) & ~0b01111111 + (uint8_t)x;
// which is what the below assembler does
asm volatile(
"mul %[width_offset],%[y]\n"
"mul %[width_offset], %A[y]\n"
"movw %[row_offset], r0\n"
"andi %A[row_offset], 0x80\n" // row_offset &= (~0b01111111);
"clr __zero_reg__\n"
"add %A[row_offset], %[x]\n"
// mask for only 0-7
"andi %[y], 0x07\n"
"andi %A[y], 0x07\n"
// Z += y
"add r30, %[y]\n"
"add r30, %A[y]\n"
"adc r31, __zero_reg__\n"
// load correct bitshift from program RAM
"lpm %[bit], Z\n"
: [row_offset] "=x&" (row_offset), // upper register (ANDI)
[bit] "=r" (bit)
[bit] "=r" (bit),
[y] "+d" (y) // upper register (ANDI), must be writable
: [width_offset] "r" ((uint8_t)(WIDTH/8)),
[x] "r" ((uint8_t)x),
[y] "d" ((uint8_t)y), // upper register (ANDI)
"z" (bitshift_left)
:);