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; Copyright 2014, Sinclair R.F., Inc.

;

; Unsigned arithmetic operations.

; Notation:

;   ux_n is the n'th byte of ux where n=0 is the LSB

;         example:  ( u0_0 u0_1 ) are the LSB and MSB of a 2-byte 16-bit value.

;   u0 and u1 are two input vectors, us is their sum

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;

; Add two unsigned 8-bit values to produce an unsigned 16-bit value.

; Method:  calculate and push the carry bit onto the return stack, calculate the

;          8-bit sum of the two 8-bit values, use the previously stored and

;          computed carry bit as the MSB of the 16-bit return value.

; 6 instructions

;

; ( u0 u1 - us_0 us_1 )

.function math__add_u8_u8_u16

  ; ( u_0 u_1 - u_0 u_1 ) r:( - c )

  ; ( u0 u1 - us_0 us_1 )

  +c >r + r>

  .return

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; miscellaneous unsigned addition operations

; ( u0_0 u0_1  u0 - us_0 us_1 )

; 9 instructions

.function math__add_u16_u8_u16

  ; ( u0_0 u0_1 u1 - u0_0 u1 ) r:( - u0_1  )

  swap >r

  ; ( u0_0 u1 - us_0 c_0 )

  +c >r + r>

  ; ( c_0 - us_1 ) r:( u0_1 )

  r> .return(+)

; ( u0_0 u0_1 u1 - us_0 us_1 us_2 )

; 13 instructions

.function math__add_u16_u8_u24

  ; ( u0_0 u0_1 u1 - u0_0 u1 ) r:( - u0_1 )

  swap >r

  ; ( u0_0 u1 - us_0 c_0 )

  +c >r + r>

  ; ( c_0 - us_1 us_2 ) r:( u0_1  - )

  r> +c >r + r>

  .return

; ( u0_0 u0_1 u0_2 u1 - us_0 us_1 us_2 )

.function math__add_u24_u8_u24

  swap >r .call(math__add_u16_u8_u24)

  r> .return(+)

; ( u0_0 u0_1 u0_2 u1 - us_0 us_1 us_2 us_3 )

.function math__add_u24_u8_u32

  swap >r .call(math__add_u16_u8_u24)

  r> .call(math__add_u8_u8_u16)

  .return

.function math__add_u32_u8_u32

  swap >r .call(math__add_u24_u8_u32)

  r> .return(+)

.function math__add_u32_u16_u32

  >r .call(math__add_u32_u8_u32)

  r> .call(math__add_u24_u8_u24)

  .return

.function math__add_u32_u24_u32

  >r .call(math__add_u32_u16_u32)

  r> .call(math__add_u16_u8_u16)

  .return

.function math__add_u32_u32_u32

  >r .call(math__add_u32_u24_u32)

  r> .return(+)